This is the tutorial to upgrade any existing server from a version prior to the 2.0.0 release to the latest
Note: it is always recommended to backup your database before doing any update.
You need first to update your server to this commit, running:
git checkout 1fc22a74088e235e78fa02decbaf0864899477d7
Now update your database as you normally do.
Update to latest master:
git checkout master; git pull;
Note: if you are using your own fork of AC, as usual, you have to sync it
Now update your core and database (again) as you normally do.