The magnification of a telescope is misleading. Useable magnification is based on the size of the aperture, aka the size of the opening in the front that the light comes through. Bigger apertures have more useable magnifications, however it is very rare that you would ever need to use the max. Atmospheric conditions and the apparent size of many deep space objects usually keep you down to 100-200x or less. Higher ones are for viewing planets and the moon and such, lower ones are to view large extended objects such as the orion nebula or the Andromeda Galaxy.
Changing the eyepiece is what changes the zoom. The "longer" the eyepiece, the lower the magnification. So if you have a 25mm eyepiece, it will have less zoom than a 15mm eyepiece.