Guy who opened mine used 2 wood saws between the door and the frame to push the catches out of the way, they were flexible enough to manipulate catches.
Al
I would find out the make and contact a local rep / repair place, I have recently fitted a new one and many of the modern ones are a much more robust design, so best find out the exact bolt location first as it may be easy
Turns out I'd better bolt the door to the deck! Brute force and ignorance was all that was required. Extremely worrying really considering it took me and a mate precisely 10 seconds to get in! Lock is replaced now and I'll be fabbing something to lock it securely to the floor with a beasty padlock after that! Cheers for all the suggestions!