I have excised for years, but my legs are not firm. what can i do to change that?

Exercise: Start an aerobic exercise program slowly. Even walking down the street for 5 minutes and returning is a beginning. Increase the time every third day until you reach 30 minutes. Your legs will likely increase in firmness as you are doing weight bearing exercise. Add half squats with low weight and if you go to a gym add leg presses. Lunges and half squats can help significantly. Best wishes.