Trying to free up memory HELP!

Hi Everybody,
I am trying to free up memory on my MacBook. I only have 3.25 GB left and I have to Software Update and I want to download some things from iTunes.

I'm trying to free up some space so I can do those things but how would I? I need to use all the applications that I have on my computer, and I need all the documents that I have on my computer. So how would I clear up some space on my computer?

I've used Clean My Mac and other computer cleaning stuff too.

Any ideas?

Thanks.