The clutch actuator is held in place with a threaded ring. Ideally, you would use a C-spanner to remove it, but access is so restricted that you will probably need to use a drift and hammer...

Now you can undo the nut on the end of the mainshaft.

There should be a pin or screw to align the clutch actuator. You will need to remove it before you can get the mainshaft bearing out. If a screw has been used instead of a pin, an impact screwdriver might help to get it out.

Now you can drive out the mainshaft bearing. It is worth replacing this bearing as a matter of course as it is relatively cheap.