The simplest method to change water is to use a syphon. There are several available from pet stores or on line.
www.drsfostersmith.com is on place to find them. The one I use hooks up to the faucet in the kitchen sink, it starts the syphon by running the sink water, pulling the water out of the tank. As soon as the syphon is going you can turn off the water and drain as much out as you want, then refill with the tube still hooked up....just be sure to adjust the water to within a 2 or 3 degree range of your tank water to be careful not to shock your fish.
A much more simple method is simply to get some tubing, and syphon the "old fashioned way".....