Unless you have a cast iron record of the service history you should definitely change the belt and rollers and any other service items. If there are any other problems you will almost certainly be able to spot them during this work.

Cheap Variator tool... Tenner on the bay...
Handle Chocked against the center stand to undo, Handle wraped in a rag and resting on the clutch bell to do up...
Can also use the tool in the clutch bell holes... go easy.
Torque wrench to do up...
Wouldnt use a rattle gun...

check the drive belt as it could be slipping or the clutch is worn out enough to cause top end speed to be affected