I have Ubuntu installed alongside Windows XP. I now only want to have Ubuntu in order to save disk space.
Can I delete XP from inside Ubuntu? If not, what's the best way I can reformat the hard disk and install Ubuntu?
This thread should help you
If you installed Ubuntu onto a virtual disk using the wubi thing, then you are probably best off just reinstalling Ubuntu from scratch using the whole of your hard disks.
If you installed Ubuntu "properly" then you are probably better off just getting rid of XP.
Quite what you want to do then will depend on your set up. If you don't already have a separate /home partition, consider using the space formerly used by XP as a separate /home.
Otherwise you could use a live Linux to adjust your existing Linux partitions, expanding your current partitions into the space formerly used by XP (if they share the same physical disk of course).