How to clean up your computer?

I want to clear a lot of space on my computer.
Do you have to do a system restore to get the best outcome?
what else can you do?
What’s the best free protection for your computer also?
Thanks 🙂
btw – I have a compaq, and windows xp
what is safe to uninstall

My school usually lets me use their virus protection for free, but just when I get a new virus on my computer the virus protection has stopped completely.

So I know it is a virus, and I just want to find a program that will do a scan and delete it and then provide some free protection? Just quick and easy fixes please? K thanks.