Looks like you have 2 Linux installs on the hard drive. Unfortunately the one your not using is hogging most of the disk space.
Are you willing wipe the drive and install from scratch? If so i would partition the drive something like this:
- / (root) 10 GB
- /home 10 GB
- swap 1.1 x ram
- /data remainder of drive.
I like to keep my data on a different partition from the OS that way if something goes wrong you can reinstall the OS and your data is out of the way.
Because Ubuntu comes out with a new version every 6 months, I like to keep a separate /home partition. That makes it easy to use partimage to make a backup of the / (root) and /home partitions before doing the upgrade.
If you can't start from scratch, it looks like you can use Gparted to shrink or delete the other Linux install partition then expand the Ubuntu install partition.
Gparted is pretty easy to use: If you have questions I'll check back later.
GParted Documentation - general
Linux.com Gparted videos