Make sure you've got gloves and a covered workspace for this step as the gearbox is packed full of grease (both the slimy solid kind and the oily "will run all over your bench" kind)

Remove the 4xH5 Bolts from around the shredder blade, the gear box will come off the motor with a light tap/wiggle.

Once this comes off the gears will be loose, so make sure you don't lose any!