The illustrations don't show the chainwheel since it's fully guarded at the front, but it may be possible to have a slightly larger chainwheel at the front. Since these are usually chainwheels without changeable chainrings, altering this could be quite expensive, and wouldn't reduce the pedalling rate (cadence) by much if the new one is to fit inside the chaincase.
From the chainline I'd guess the freewheel at the rear is an 18 tooth one. You could check that by counting the teeth, and if it is an 18, you could have it changed to a 16 tooth standard freewheel. Since the motor cable entry is on the opposite side, this is quite a simple job which many bike shops can do for you. That would reduce your pedalling rate by a moderate amount at a low cost.