Cannot Download Anything On Laptop?

I recently tried downloading iTunes as I accidently deleted it. But when I tried I got a message telling me that I can't download it because the content of the folder cannot be changed. I thought this was a probably with iTunes so I went to download something else. And I still got that message. I searched the net for answer, I found one telling me that I had to untick the "Read-Only" box, so I tried but the box wasnt ticked. So then I tried ticking it then un-ticking it, but I still have this problem.