Ubuntu 11.04 -> 12.04

[UBUminJ]

I am running Ubuntu 11.04 as dualboot with WinXP.

I am thinking to exchange 11.04 for 12.04 when it is out. When I installed 11.04, I failed to just delete 8.10 and install the new one. Probably, I failed as I didn't understand the necessary vocabulary for doing it.
What steps would be necessary ?

At that time, I also would like to reduce the amount Windows is taking. Is that possible ?

Thank you for any advice and/or links.

[zvacet]

Before you shrink Windows partition defragment it few times.After that you can resize it during Ubuntu installing proces.Now about ubuntu.If you don´t have sseparate home partition it will be good to make one.Read http://www.ubuntugeek.com/how-to-create-a-separate-home-partition-in-ubuntu.html. (http://www.ubuntugeek.com/how-to-create-a-separate-home-partition-in-ubuntu.html)
When you have separate home partition you can install Ubuntu 12.04 on partition when your /root is ( your existing partition).during install DO NOT FORMAT HOME PARTITION.