Hello tankers,
This video goes through the process of changing your gearboxes on your Tiger 1 tank and some tips I have acquired on the way. Even though this is a Tiger 1 tank, once the upper hull and tracks are off the process is the same for all of the tanks.
Start by removing the tracks, we have another video here on that:    • How to remove tracks on a Taigen Tank  
Then remove the hub cap (if applicable).
Next unscrew the 2.5/3.0mm hex screw from the drive wheel.
At this point you should be able to remove the drive wheel off of the gearbox shaft. If you cannot, please follow my tip in the video on how to remove the drive wheel safely without causing harm or damage.
Next unscrew your gear boxes from the lower chassis.
You can now remove the gearboxes from the tank.