dave123 welcome to the rvforum.
Replacing may be a challenge for you. If your cable looks rusty may just need to have WD-40 sprayed on cable and turn gear mechanism. You may also find when you look under PU a metal channel that holds your cables. On this channel there are maybe one or two Zerk fittings waiting for grease to be pumped into them to make it easier for cables to do their function, raise the roof easily.