You can uninstall it in Synaptic, even if you've installed the PUEL it
still appears in Synaptic and can be removed there.

I've found that some releases require the old version uninstalled, but
most don't.

I used Synaptic to completely remove VB version 3.1.8 and then installed the new
version 3.2.2 and when I opened Virtual Box my Windows XP was intact and working
good.

Yes, the program is uninstalled but all its settings and folders are intact.
And the virtual hard disks, also. It is so with other programs, also.

I do not like the EULA that Oracle has forced on us. The previous version
did not have it. It said by downloading you agree to the license. It is
their righ of courset, but it is contrary to Linux and emphasizes that
Oracle is an open source newbie and outsider. We have an alien in our midst.
Will OOO be next?

I looked there and did not find it the first time I looked.

Here is the best way to update, IMO. I just did it and it worked without a
hitch.

1. Add to /etc/apt/sources.list one of the following repositories depending on
your installed Ubuntu version.

deb http://download.virtualbox.org/virtualbox/debian lucid non-free (10.04)
deb http://download.virtualbox.org/virtualbox/debian karmic non-free
deb http://download.virtualbox.org/virtualbox/debian jaunty non-free
deb http://download.virtualbox.org/virtualbox/debian intrepid non-free
deb http://download.virtualbox.org/virtualbox/debian hardy non-free
deb http://download.virtualbox.org/virtualbox/debian lenny non-free
deb http://download.virtualbox.org/virtualbox/debian etch non-free

2. Open a CLI and type sudo apt-get update <Enter>

3. Back up /home/<yourusername>/.VirtualBox

4. Open System->Administration->Synaptic

5. In search box type virtualbox

6. Select and install virtualbox-3.2 - The previous version will be removed and
the new version installed.

When you next start Windows XP, you will be prompted to update Guest Additions,
if you have it installed. Just follow the prompts.

This information came from http://www.virtualbox.org/wiki/Linux_Downloads