Yes defragging is found on the accesories menu in system tools, but your cache memory is full because of all the programmes taking up the memory, you need to install more memory.

Run this tool to tell you whats fitted and what type to buy, it's very easy to fit more memory and will speed up your system also, it's cheap, and if you take it to a shop to fit they will charge around £15.00/$30.00 to fit it when it's easily done, take the side off and look for the memory strip and there will probably be a spare socket to fit another one or remove current memory and replace with a larger amount