Try to wipe the cache partition. This works on most Galaxy S phones, and it's harmless. It might make the phone a bit more snappy, especially if you've never wiped the phone before. This doesn't do anything to your data, picutres, or contacts. It's just like a temporary storage spot.
power off the phone
hold down the volume up + home + power all at once
wait until the boot screen comes up and it will says recovery in the top left very small, let go at this point
use the volume up and down to scroll and use the home button to select
choose wipe cache
than choose boot system
