The easiest way to delete everything and start over is to put the Ubuntu thumb drive back and and let ubuntu format and reinstall.
in my install guide I make a note
(excellent point to create a backup image)
The reason for that is I have probably installed this 30+ times experimenting with different settings, mostly involving the sample config files. There are lots of ways you can create a backup image, but sometimes creating a backup image could take just as long as starting over at square one if your not familiar with the process, and there are lots of different ways to go about making a backup that you can restore from.
A graphical approach would be to use RedoBackup, the easiest way to make use of it would be to format the drive using less than half the drive space during install (in server this has to be done manually, if i recall correctly, the automatic methods are usually something like use all available space or use entire drive, so the manual option has to be selected) With half the drive available, you launch RedoBackup, use the partition tool to create a second partition with the rest of the available drive space (the other half of the drive) then RedoBackup can backup partition 1 to partition 2.
Once the backup is in place, you can at any time stick the RedoBackup thumb drive in the computer and restore from partition 2 back to partition 1.