Next undo the bolts that hold on the end cap...
...and if the cap is stubborn to remove use a puller.
Don't be tempted to pry this bit off. The main casing is steel and the cap is a nicely cast piece of aluminum alloy.
When you've got the cap off you will be able to see the commutator and the four brushes.
At the other end of the starter motor remove the nut and bolt that holds the actuating arm in place.
This actuating arm is the bit that gets pushed by the solenoid and engages the starter motor driving cog into the flywheel.