Bit of a pain in the bum but
there are 6 (I think) rivet heads that you can see if you turn the thinh upside down. Carefully drill them out - taking care not to damage the plastic washers that come with them. Then move to the locking hooks. Drive out the pins that hold the rubber/sponge bump stops and take these off as well. The lock will then come out.
Installation is the reverse but remember to put on the washers for the rivets sand to clean out any swarf in the mechanism.
I'm sorry but I can't remember the rivet size - BM do a kit but its pricey.
Paul