While you might always just try a different exercise, we like DailyBurns tips for modifying some classic moves.
(Do a full set before switching sides.)
Another helpful tip is to do squats with your back on an exercise ball on the wall.
Check out the link below for more modifications.
5 Workout Modifications to Go Easy on Your Knees| DailyBurn
Photo bywww.localfitness.com.au.