Hi John,
Remove the roller by removing the end nuts on either side of the lawnmower. You will need to remove the side panels of course which are held in with allen key bolts. Once the panels are off you will see the 2 nuts holding the roller axle in place, it then just slides out towards the bottom. The new roller plate will then fit in.
andrewmartin5286 'at' g m a i l . com
Andrew Martin, May 2013