Usually not hard. The blade and seals are held in place usually by 4 bolts. Since there are several bramds of valves you first need to identify the brand you have. On my fiver I had to drop part of the underbelly to access the valve. Take the 4 bolts out, work the 2 halves apart. I loostened the Furnco fitting to slide one end apart. Drop the old blade and seals. Grease everything up using lots of plumbers grease, slip it back together. Carefully check to be sure the seals ha e not shifted, put the 4 bolts back on. Tighten very evenly. Dump in maybe 5 gallons of water and check for leaks.