How do I replace the rear shifter on my mongoose efx 21 speed 26" bike

SOURCE: Where can I find a drawing of a 21 speed 26

http://www.amazon.com/gp/product/images/B000B8IDS2/ref=dp_image_text_0?ie=UTF8&n=3375251&s=sporting-goods If it has a Shimano Altus rear derailleur, you can look here:http://bicycletutor.com/adjust-rear-derailleur/comment-page-3/ or here:http://www.parktool.com/repair/readhowto.asp?id=76

SOURCE: How can I raise handlebars on a 26 in. Mountain

You need an Allen wrench (a.k.a. hex key) to fit the bolt head right in the middle of the handle bars. Loosen this bolt just 2 or 3 turns then tap the head with a soft hammer or block of wood and a hammer. Then pull the handle bar stem up (and all of the way out so you can see how the wedge-shaped nut at the bottom of the stem works). Look for a mark on the stem telling you how high you can safely raise the bars (you have to leave enough of the stem inside the tube so that it will be strong.) Put it back in and tighten it up. If you found this helpful, please vote. Good luck

SOURCE: How to change gears?

if the gears are anything like mine, they are on the handel bars and all you have to do is turn them untill the arrow points to the number you want.

SOURCE: i have a mongoose dxr

http://www.parktool.com/blog/repair-help/categories/derailleur-systems