Imagine that you are in Spain and you want to tell the driver to go faster or slow down. These are the phrases you should use:

Puedes ir mas rapido por favor?
Puede ir mas rapido por favor? (formal)
(Could you go faster please)

and also:

Puedes ir mas despacio por favor?
(Could you go slower please?)
or just use:
Mas rapido! (Faster!)
Mas lento! (Slower!)
Reduce (Slow down)
Para! (Stop!)