When you run out of disk space, you can either clean up your harddrive or migrate to a bigger one. On a physical machine, you'll have to buy a bigger harddrive. On a virtual machine, you can create a new virtual disk and migrate to that.
The migration Edit
Insert new disk Edit
The first step is to insert the new disk you want to migrate to, whether it's a physical or virtual disk.
Migrate data Edit
Then to copy the data:
dd if=/dev/sda of=/dev/sdb
After the migration the partition will be the same size as on the original disk, since it's an exact copy. So we need to expand it.
Expand the partition Edit
Ubuntu live CD Edit
If you're on the Ubuntu live CD, you can use gparted, which can expand ext3, ext4 and NTFS filesystems among others. Just open gparted, choose the right disk, right-click the partition and choose resize.