Reinstalling Windows 7

I've been having problems with my laptop and can't seem to figure out why. I'm at the point where I just feel that I may need to reinstall Windows 7, but need instructions and guidance on this. Can you help me with it? I would sincerely appreciate it as I can't use the laptop the way it is. It is very very slow, can't seem to download programs etc. Please advise.

Thanks!