As SpecialX suggested, if you don't already know the answer to all these questions you're asking, I'd strongly suggest not mucking with your bike to improve its performance. If you want it to go faster and further -- pedal harder.

Though you could take it back to the e-bike store and talk to them about it. Increasing your range is fairly straightfoward -- they sell you a spare battery pack and maybe a mount to hold it on the bike if there isn't already one, and then you just swap batteries as needed. Increasing speed is more complicated.