Ive had to change my after market levers for the standard levers before i part x'd the bike, so this is me taking my aftermarkets for the standard ones.
Remove the screw using a T35 Torx bit and an 8mm spanner to remove the nut underneath
Carefully pull the ball from the cup by pulling the lever away from the bike
This is the cup that you are freeing the lever from:
Next you will need to remove the copper sleeve to allow the ball housing the come away from the lever. I tend to use a screw driver that gets wider further down the shaft to drive the sleeve through out.
Then you will be ablwe to remove the ball housing
At this point you need to be aware of the spring, once the copper sleeve is removed the ball housing will come out and the spring will fall out too, spring hole is the round hole at the bottom of the pictured lever:
Next you need to remove the adjusting screw from the lever, remove the end cap by prising apart with a screw driver:
Then spin the threaded shaft out of the lever
To reinstal new levers, do the opposite ! (Easier said than done when fighting against the spring )