IF the 4420 is the same as the 7720--only belt on the whole combine that is easy to replace.
On my 7720, I took the belt & chopper off for corn every year. I simply grab the lower belt near the straw chopper and pull. The idlers behind the fuel tank will turn against the spring, allowing you to flip the belt off the straw chopper pulley. Let go. Now, work the belt off the idler pulleys (sometimes its tight to fit between the pulley and the brackets, keep the belt flat so it slides out). Then go around the front of the clean grain elevator and slip it off the inner side of the driver pulley. It should pull right out.