Anyone know how to get rid of unwanted files such as junk?

I was wonderig if anyone knew how to ge rid of unwanted files and junk. Ive been dealateing them into the recylce bin. But that doest do any good. It keeps coming back And if i get rid of all this junk would the computer work much faster? Iam not looking for a program off the internet, but i know there is away on my computer on how to get rid of unwanted files. The typ of computer i have is a dell windows XP. Incase if yall ask. Thanks for the help.