My computer is very slow, how do I clean it up?

You can try to do this following steps in making the computer fast.
First what you can do here is to free up some resources on your computer system, you cna do that by uninstalling some programs that you don't really use , doing that will definitely improve the sped of the computer.
Then do a defragmentation on your hard driver , you can find that under programs> accessories > system tools, then finally if you really want to improve and make the computer to work faster adding some memory on it will be the best thing to do.