Replacing a Novoferm garage door lock
That's a Euro-style lock cylinder. It is normally held in place by a setscrew clamping it into the lock, but you may have to substantially disassemble the lock before you can get to that screw.

If you can't figure out how to remove the cylinder, I'd suggest dismounting the whole lock body from the door and bringing it to a locksmith. That will save you the "on site service" fees.

Rekeying double-sided Euro cylinders is a skill not all locksmiths in the US have. Single-sided, with keyway on one end and thumb turn on the other, are simpler.