You can read the official news announcement at:
To upgrade your OpenSUSE 11.3 installation follow the simple steps below.
Open a terminal / console and type the following,
Enter your root password, then type or paste the following commands,
zypper addrepo http://download.opensuse.org/repositories/KDE:/Release:/45/openSUSE_11.3/ kde-4.5-stable
You will see the following question, do you want to reject the key, trust temporarily, or trust always?
Press 'a' to accept the key, KDE will now begin to update. When the installation has completed, reboot your system.
It should all be working perfectly after the reboot but if it does go wrong, don't blame me!
Enjoy KDE 4.5!