First Check all partition:
$ df -h
The fastest way to locate your folders that are too full is by narrowing down the folder file size in levels from the root folder. You start with the root folder by:
sudo du -h --max-depth=1 /
Then - EITHER you increase the depth, i.e. the levels below:
sudo du -h --max-depth=2 /
OR - quicker - you you look which folder has eaten up the most disk space, and do the same on this folder:
sudo du -h --max-depth=1 /home/<user>/<overfull-folder>
Once you found it, just remove that one:
rm -rf <path to overfull-folder>