Flip your phone over so the screen is facing down.
About half way down there is a small button with a few groves. Push this button in an upward fashion. This will release the battery from the back of the cell phone.
Once the battery has been removed, you will need a small Phillips 60 mm screwdriver. Remove the two 1.2mm Phillips #1 screws on the back of the phone.
Use a spudger tool to pry apart the phone. It may be a little difficult to pry open. Use the flat part of the spudger tool and go all around the phone. It will come apart.
Once you have the phone apart simply remove the key pad and replace it with the new one.
Don't forget to put the screws back in. Place the battery back on the phone.
Push the two parts of the phone back together. You will here a loud click when the phone is back together.