Yes you can change the belt yourself if you are a bit of a handy man...
If in doubt pay someone to do it for you.
1. Unplug the unit from the wall.
2. Remove the motor cover or hood.
3. Locate the screws or bolts that are used to adjust the belt tension. They are normally on either side at the rear of the treadmill. Loosen both sides and push the rear roller toward the deck.
4. Loosen and remove the front roller. If your treadmill inclines, turn on the power and raise the treadmill a few degrees so the roller can be removed. After the front roller is removed, remove the rear roller. Youu are now able to remove the belt.
5. Take off in one piece rather than cut it of
6. Along the sides of the treadmill you will find bolts or screws that hold the deck in place. Remove these and lift the deck and old belt out together.
7. Lubricate the deck.
8. Normally the belt should be installed so that the seam goes downward from left to right, much like a backward slash. Some belt manufacturers will mark the belt on the inside with an arrow pointing in the direction the belt should travel.
9. Slide the belt over the deck in the proper alignment and lay the belt and deck together back onto the treadmill.
10. Start all of the screws or bolts before tightening them securely. Decks tend to get warped after a while so you may need to push or pull a little to get the screws started. I have found that it is a good idea to install the rollers before securely fastening the deck to the frame.
11.Pull the belt to the rear of the treadmill and slide the rear roller through it. Start the adjusting screws in the roller just enough so they do not fall out.
12. Slide the front roller inside the belt and replace the drive motor belt. Do this before you tighten the roller. After you get the front roller tight, then tighten the rear roller with the adjusting screws. Tighten each side equally until the belt is snug on the deck.
13. Turn the treadmill on. If the belt start moving to the left or right adjust with the two adjustments at the end of the deck
14 When running true carefully step on the treadmill while holding the side rails. If the belt stops then you need to tighten it more. Step off the treadmill,and tighten each screw one full turn and step on the belt again. Repeat this until the belt does not stop.
15. Increase the speed to a fast walk, hold the handrails and apply downward pressure as you walk on the treadmill. If the belt stops or hesitates then adjust some more. Now increase the speed to a jog, probably around five or six kph. If you feel any hesitation in the belt when your foot hits it, adjust it some more. Continue until you are certain that the belt is not slipping.
It is an involved process so again if in doubt pay someone to do it for you...