How do I make one computer my main Steam account?

I have a desktop and laptop, and would like the desktop to be the main account - when I change library settings I want the laptop to sync to it, etc.

Currently it is the other way around - when I change categories on my desktop, once I log into my laptop when I'm outside, the settings all revert and when I go home they have changed on my desktop (reverted). When I change my username this happens as well.

Any help would be much appreciated, as this is giving me a big headache!