Removal and installation is really straight forward and there is only a few extra steps. I keep my drivers in separate folders for each version. All commands are displayed as if you were in the working folder for that driver and ONLY that driver version.

Generate the fglrx/catalyst drivers for your distribution
Supported distro’s found here.
sh ati-driver-installer-* --buildpkg Distribution/codename

Backup your xorg.conf (just in case, re-configuring xorg sucks!) and remove the previous fglrx drivers
sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.bak
sudo apt-get purge xorg-driver-fglrx fglrx-kernel-source fglrx-modaliases fglrx-amdcccle
# if /etc/ati still exists, remove it!
sudo rm -rf /etc/ati/

Now reboot and when restarting do not boot into the GUI. Xorg will be looking for your fglrx driver and it is now obviously gone, so you will either lock-up or it may recover nicely and allow you to enter into a low graphics mode. Either way, boot into a terminal window. On Ubuntu you can enter the recovery console.

Now from terminal install the new fglrx/catalyst driver
sudo dpkg -i xorg-driver-fglrx_*.deb fglrx-kernel-source_*.deb fglrx-amdcccle_*.deb

Now reboot from terminal and enter the GUI. You will have to reconfigure any settings you made in the previous Catalyst driver. fglrx/catalyst brightness, contrast, gamma howto.

If you happen to have any issues booting back into the GUI. Go back to the terminal and remove your previous xorg.conf. and follow these instructions for generating a new one.

A more detailed walk-through can always be found at http://wiki.cchtml.com/