How to increase the partition size of Ubuntu installed under Windows? [duplicate]
Solution 1:
As Marky suggested in the comments, you can resize the disk image of a Wubi installation using any of these methods (written by bcbc).
Alternatively, you can free up space in your Wubi image by moving some of your documents or other files like music, ebooks, or videos (just not programs or system files) to the host Windows system's partition (accessed as /host in your Wubi system).