How do I remove this lock cylinder?

[OldKettle]

Hi,
I would like to replace the existing cylinder in an aluminium door with an anti-snap lock, but I cannot figure out how to remove the existing one.

I have replaced a couple in the past, in uPVC doors, but could always locate the screw to release the existing cylinder.

There are a couple of screws above and below the lock, but removing them seems to have not effect and I can find nothing on the assembly to allow it to be dismantled (no Allen key slots etc).

Before I start popping bits off the assembly, can anybody please advise?

Any help would be much appreciated.

Below are a couple of pics, one from the inside with the door closed and one taken from the side (inside is on the left hand side).

EDIT: Never mind, just figured out that I needed to remove the strip down the inside of the frame, to expose the housing. Not quite sure why I only realised that as soon as I posted!

 

[OldKettle]

I've also just realised that, because the locks are UK Oval, rather than Euro Cylinder I can't get anti-snap cylinder anyway.

Should I just replace the whole lock? Can anybody suggest a good replacement, please?

If I am replacing the whole lock, do I need to stay with a cylinder or can I switch to a 5 lever mortice? (not sure if I could do that and get away with keeping the existing handles).