I was wondering if it was possible to convert from YAF to myBB and if so how? I searched all over the internet and could not find out how. I am running the latest version (1.6.3) of myBB.
Not currently. You've to wait someone to make a merge module for you.
Alternatively, you can merge YAF to any other forum like SMF (if its available) and then convert it to MyBB.
I can't find YAF converters for any forum. Take a look at the database and see if you can find a forum with a similar database setup.
YAF is not, and will not be, officially supported at this time. If someone wants they can make an unofficial script for this.