There was a tutorial knocking about on here before.
Failing that, you need to remove the armrest by taking out the ash tray ( I think, it's been a while since I did it) which will reveal an allen head bolt, then inside there are some small torx screws, they're well hidden as they are covered in the same flock as the inside of the rest. Removing these screws should release the catch, then you will be able to see where the tab has broken off in the mechanism, simply drill this out, then I cut the head off a machine thread screw and drove it in, bit of Araldite and it's worked ever since. Might as well break off the other side and replace that too, it'll only break eventually.