Are there any?
Any noob-friendly tutorials on how to upgrade?
Do I have to deactivate my plugins?
Download the zip, and open it up, there should be a readme on upgrading from 6.0
yes deactivate all your plugins but read that file first.
Where can I download the updated MyBB 1.6.1?
No, download from,
http://mybboard.net/download/128
It's the change files from 1.6.0 to 1.6.1. You don't need to re-upload every file again, unless you're upgrading from 1.4.
I've downloaded the change files, what am I gonna do now?
Upload them overwriting original.
My templates got reverted
What version did you choose on the upgrade script?? This upgrade doesn't revert all your templates.