I had this problem too...
The best way is to check out your "home" folder (in /root/home) with the app called Storage Usage. This can be found in the repos.

You can see how big each folder is, so you can immediately see which app is huge and is ready to get deleted.
The best user friendly file manager to access your /home/ directory, is Cute Explorer (also in the repos)


Secondly:
I saw that I had 500mb of unnecessary cache from apt get... I deleted those in xterminal with the following command: apt-get clean

I hope the 2 advices will help you