What's an inexpensive way to increase my e-Bike's top speed and driving range?

I recently bought one of those $600 Ancheer e-Bike's with a 36V 8AH lithium battery and a 250 watt rear hub motor. I love the bike. It's light, and a great deal for the money. But, I would like to increase the range and top speed. It looks like the easiest way to increase the driving range is to...