My toms are beginning to sound dull and worn and I want to change the sound to a fat deep sound but im afraid if I tune down the skin wont sound as good after it was stretched by tuning it up. Do I need knew skins or should I be fine just tuning down.

You won't know unless you try. Sometimes old heads don't like low tunings because the bowing caused by being played for several months creates all kinds of nasty vibrations and overtones. Give it a shot - if you don't like it, you can tune them back up again until you can get some heads that will do the job. No harm in trying.