Free upgrade (if that is what it should be called) to Win 10 from 7

I bought a new desktop in June 2012, w/Win 7. Now there is an upgrade to Win10 icon, is in the lower right corner. The upgrade is supposedly at
no cost. It works great, does everything I need and is very fast.  I have heard rumors that Win 10 has a lot of malware.  And there is no way to
prevent Win 10 from keeping track of your browsing history. I'm also concerned it may slow down my PC. I use an antivirus given free by my ISP.
On the other hand, if I don't upgrade now, I may have to pay later. And Win 10 will be supported a lot longer.

So, I guess I have no real choice. Are there any other problems or disadvantages to the upgrade?

In the past, you could always reload the OS and start fresh, if you had a problem. I have never done that w/Win 7. I have not  formatted a hard
drive and/or reloaded an OS in a long time. Win 7 takes 3 Disks, which I have, but I'm concerned I may have problems doing it. I get the feeling
PC makers & MSFT don't want you fixing your own machine anymore. They want you to buy a new PC & OS instead.

Hi Doug,
Windows 10 is much more secure than Windows 7. And windows 8 (and probably 10, too) actually run better on most old Windows 7 machines than did Win7. In trying to create a single OS for use on phone, tablets, and PCs it seems that they needed to make a Windows that accomplished more with less.
Before upgrading any system, go get a USB external drive and back up your desktop's hard drive to it. Be sure to also make a system image backup, which is a separate process. This is just basic good practice for regular use, but is especially advisable before performing a major system update.
When you upgrade to Windows 10, a copy of your Windows 7 system will be put on your hard drive for 30 days, so you can revert if necessary. This is in addition to the backup on that external drive that you just made, and the original Windows 7 DVDs you still have.
Don't worry about having to format a disk. The upgrade or re-install processes, including disk formatting, are highly automated and seldom require more from you than a few mouse clicks.
Windows Defender and Windows Firewall, the native protective services in Windows 10, are perfectly capable of keeping your machine secure from external threats.
These days most malware issues are what is called "behavioral" in origin. That is, an email or web site tricks you into allowing the bad stuff to be downloaded. Clicking on any link is like pulling the trigger on a gun. You have a responsibility to know what you're doing and why, or don't do it.
I work remote full-time and haven't used a third-party anti-virus product in years. But I don't open email attachments unless I know exactly what they are and who they're from. I never click on a link in an email supposedly from my bank, broker, or any other site. And I never click anywhere in any "fix this" or "find out more" type links in "warnings" that pop up to tell me that my system has a problem. When installing new apps I am careful to opt-out of any optional crapware that may come along for the ride. (That's one of the ways you end up with some search engine you've never heard of replacing Google or Bing)
If you exercise care and good judgement in your online behavior, it's almost impossible for malware to get on to an up-to-date Windows machine. I regularly run MalwareBytes to check for bad things that may still have found their way onto my machine, but it hasn't found a single bad guy in my system for years.
One more behavioral security tip: I have friends and family members who make a hobby out of forwarding things to all of their family and friends. You know the kind of email I'm referring to - those funny pictures or stories, or long political/religious editorials laced with pictures and garish typefaces. I never open those emails. I have a filter set up on those relatives' addresses that automatically trash any forwarded email from them. Emails that they originate get through, but the junk doesn't.
There are several on this forum who are more up to speed than I on the best practices for Windows installation and configuration. They may have additional/better advice.
Finally, as for activity tracking - I understand those who feel concerned about this. For myself it just isn't an issue. If there are people out there all that interested in what I as an individual am doing online with the intention of using that knowledge to do me harm:
1. They are going to be mighty bored and
2. I doubt that they would make their snooping as well known as Microsoft has.
3. My cable company, email service, Google, bank, credit card providers, SunPass and a host of others all know significant details about my activities. I fail to see what difference it makes if (and it's a big if) Microsoft is one of that bunch. 

If you use Windows Media Player, it will not be there in Windows 10.
Just an FYI...

Windows Media Player installed with my Win 10 - it's in the Windows Accessories folder when you scroll down the ALL APPS list.

I have three Win 10 systems now, one upgraded from Win7 and the other two from Win8.1. Am happy with all of them.

I think most of the moaning about Win10 is simply that it is not Win7 or XP. I get that, but things change, and overall get better.

No "malware" that I know of, but some people don't like the privacy defaults on some features. There are ways to change all of them - just Google Windows 10 and your pet peeve and there will be plenty of advice on how to "have it your way".

  Just a suggestion. I have An older Dell with Win/7 PRO and i checked their website and it is not compatible for Win/10. My two Acers one had Win/10 Ultimate is now an Win/10 Pro ; the other was 8.1 Home and now Win/10 home; they work fine! Check the manufacturers website as the Win/10 icon said my Dell was compatible and wasn't so that will stay at 7 until I know it's OK.