1 Autobuilds are nightly builds of the latest code. They have the latest features, bugfixes and assets but they could be less stable than regular releases.
3 If you "installed" Xonotic by downloading and unpacking the [zip](http://xonotic.org/download/), you can update a regular release to autobuild using the scripts located in `misc/tools/rsync-updater` (use `update-to-autobuild.bat` if you're one Windows, `update-to-autobuild.sh` on Linux and Mac). You can go back to the normal release using the `update-to-release` scripts.