I'm using OpenSUSE 11.2 which has Qt 4.5.3.
Can I update its Qt to version 4.6? If yes, how?
Any reason you want to update? I'd recommend keeping it as it is.
su root && zypper ref && zypper up
should update all your packages. I say all because there are lot of interdependencies on Qt version - I'd probably leave as it is.