This is easiest if you first remove the door. Whilst supporting the door, remove the 3 cross-head screws connecting the door to the hinge, then slide the door off the hinge. The front cover of the door can then be prised off using by inserting a table knife lengthways in the door edge where the front cover meets the main door body and gently working your way around the door edge, twisting the knife slightly to ease the cover off. The cover should then be completely removed, withdrawing the old handle (if necessary) through the slot in the cover.
You will now see that the door lock mechanism is held in place by two cross-head screws clamping the ends of the spindle. Before removing, note the position of the spring. Now make sure the ends of the spindle in the new handle mechanism are protruding equally at each end and fit the new mechanism, making sure the sping is in the correct position.
The door cover can then be repositioned, guiding the handle through the gap provided, and then firmly press together around the edges.
Re-fit the door to the hinge - and you're done!
Ken L, January 2007