Why not just upgrade?
Open the /etc/update-manager/release-upgrades file and set Prompt=normal (you will need super user privileges – sudo). By default, this is set to lts, which will only prompt when a LTS upgrade is available.
Once you have done that, go back to the Update Manager, and click Check button. Now the Upgrade to 10.10 button will appear.
If you want to do a clean ubuntu installation then on the disk partition screen select your old ubuntu install partitions.