Stuck in update boot (not enough disk space) I'm currently having a Macbook Air 120GB SSD where I tried to update the OSX to El Capitan. Very first it did not want to update due to lack of disk space.

After I cleared up some photos so it had around 3-4 GB available space, the installer of OSX launched and started loading, after few minutes it booted into a setup-only mode, where you only see the setup and select language and click next-next-next, but at this point it now stops me saying "not enough disk space".

That's fair enough, but now I'm stuck in this bootmode, if I turn off or reboot my Mac, it reboots into this installer again and I can't really exit and get back to my OSX to delete more files to free up some diskspace. I'm basically stuck in the updater itself when booting.

Any suggestions how I can get out of this boot and back to the original OSX, so I can free up some space? Thanks in advance.
Go in the Recovery menu (hold cmd+r), in the top left corner, you should see the Apple logo. Click on it and select the boot disk, which should appear as your internal hard disk, you will be prompted to enter your password to decrypt it and you should be good to boot into your old system.