Pretty easy to do. Turn the main water off. Flush the toilet and hold the handle down to get as much water out as possible. Use an old towel and bucket to get the rest out so you want have a large mess on the floor. Cut the plastic line between the valve and the toilet. Hold the pipe coming out of the wall and with the other hand slightly pull and twist the flowtite counterclockwise. It will come off.
I replaced all 17 of those valves in my house with the all metal:
Glue on Brasscraft valve. They are 1/4 turn valves and should it ever become necessary, one can repair or simply unscrew the valve from the glued PVC connection and replace. Never have to cut the pipe or anything in order to repair. A little pricey compared to others but some others cannot be rebuilt. You'll also need a new hose that goes between the valve and toilet.
If you want to do all of them, there will be 2 at each sink (bathrooms, kitchen, utility), 1 at each toilet, 1 for dishwasher, and 1 for refrigerator.