It will be listed in your owners manual at what speed to shift up.
Heres some tips from an energy saving website
QUOTE
After starting the engine, it is best to drive off immediately. Idling causes pollution and excessive fuel consumption.
Depress the accelerator gently to drive away and change to a higher gear in time.
Do not approach traffic lights at speed. If it is clear that you will have to stop, begin slowing down well in advance.
Even if you only have to wait for 30 seconds, it is more economical to switch the engine off and start it again when necessary.
To drive economically you need to maintain a sufficient distance between yourself and the next vehicle. This way there is less need to react suddenly; you can brake and accelerate more smoothly.
Avoid over-revving the engine unnecessarily and drive in a gear position suitable to road conditions.
On bends, reduce speed in time and accelerate smoothly when you are halfway through a bend. Late, heavy braking before a bend followed by rapid acceleration leads to excessive fuel consumption.
If you watch the roads ahead and anticipate any likely problems, your driving style will become smoother and better controlled.
Save energy website