problem with updating

Hello, I've got a slight problem. Again. On my computer it is shown that there is a new version for download (Version 3.0.10). But when I try to install it it tells me that the newest version is already installed and ends on error 1: File can't be copied. (don't know the exact words for I'm using the German version). Again. Had the same problem just a month ago.
Why is it that I'm not able to update the site by myself without having to ask for help?