Push down on the top of the xylophone bar, this will make the bottom of the bar come loose and stick up in the air. At the top of the xylophone bar is a rubber pin that holds the bar in place. The bars are set upon two metal braces with the tops of each xylophone bar extending over the edge of the brace. Because of this, by pressing down on the top of the bar, the brace acts as a fulcrum with the bar and pushes the bottom of the bar into the air.
Grab the top edge of the xylophone bar and pull the bar toward you to remove the bar from the xylophone brace. This will prevent damage to the rubber pins that hold the xylophone bars in place. If you pull from the bottom, which is the distance furthest from the pin, you can cause undue stress on the rubber pin.
Insert the new bar you would like to use by pressing the top of the bar on to the rubber pin and then allowing the bottom portion to fall into place on the xylophone brace. The guides on the xylophone will ensure that the bar is aligned properly. You can order additional bars from a local music store or music instrument catalog such as the "The Woodwind and Brasswind." If you order enough bars, you can change the entire range of the instrument down or up as much as a major third.