Can't update any apps on my Macbook

I have a Macbook Pro with OS X 10.8.5 right now, I'm trying to update it to Mavericks but it always downloads a bit then says an error occurred. Also, my iTunes wasn't updating as well so I tried to reinstall it but now it won't install again. When I try to update in on the app store there is an error and when i download the file from online it says 'image data corrupted'.