I’ve noticed that my PC is a little slower than usual. What’s the best free program I can download to clean up unwated files and clear up disk space?

A free program would be preferred.

What is a good free program which can clean my PC or registry?

I am selling my computer and I want to make sure that everything is wiped clean before I sell it. How can I totally delete everything to what it was when I bought it? Do I need to buy something or is there a free program that will delete everything? I just want to make sure that nobody can get any of my personal info from it.

i need a free program that will get rid of stuff that has been deleted from my add and remove programs but still in my hard drive please help me