"History... definitely history." Rainman.

Oh wait... you're 13, you probably haven't seen rainman.

Pony is right defintely need to trim down history. Also watch any texture files you may have assigned. The texture file resolution down too. To help speed things, up, user layers. once you have items assigned to layers, turn off the visibility of layers. In your project folder you can safely delete any renders you no longer need...

any other suggestions?