When upgrading Ubuntu from 11.10 to 12.04 I discovered an unexpected problem. The upgrade was stopped because there wasn't enough free space for the installation. I managed to free some space and do the upgrade but now a prompt appears after logging in saying I'm out of space. This prompt asks me if I want to examine the problem. The "Disk Usage Analyser" is opened. In the top it says:

Total filesystem capacity: 47.0 GB (used: 13.5 GB available: 33.4 GB)

Folder -- Usage -- Size

• / -- 100% -- 12.5 GB
• • usr -- 44.8 % -- 5.6 GB
• • home -- 30.3 % -- 3.8 GB
• • lib -- 13.0 % -- 1.6 GB
• • var -- 9.1 % -- 1.1 GB
• • boot 2.5 % 309.5 GB
• • and a lot of small contributors like: etc, opt, sbin, bin etc.

I do not really understand this problem since the analyser in the top says that I have 33.4 GB left in this file system. What can I do to make Ubuntu use the remaining space?

Running df -i in the terminal gives:

Filesystem      Inodes  IUsed   IFree IUse% Mounted on
/dev/sda7       610800 576874   33926   95% /
udev            213451    563  212888    1% /dev
tmpfs           218524    486  218038    1% /run
none            218524      3  218521    1% /run/lock
none            218524      7  218517    1% /run/shm
/dev/sda8      2264752  16371 2248381    1% /home

What does this mean?