To do this task without the risk of damaging your paint you really need the BSA suspension servicing tool part number 61-3503. This can be obtained from Lightning Spares
There are two types of retaining collars
Fig 1 ( one piece collar) will be difficult to remove without the service tool fig 2 (split collars) can be removed more easily. In either case set the unit to its softest setting. You will need an assistant to push down while you release the collars. Having got the collars out you can fit your new parts. You will find it more difficult to refit the collars than to remove them. This is especially likely with the single piece collar. Anyway good luck.
John
