Hi there. Had to repair mine today as the cable snapped out of the drum and machine.
You prise the wheels off by using a big flatbladed screwdriver. Then undo the two torx screws that sit inder each of the wheels. Then you will need to undo the T-15 Torx screws on the body of the Dyson - one on the front and one on the back. (I had to buy a set of Torx drivers from my local car accessory store to reach far enough in to do this.) Then lift the front/top cover off and you have access to the cable drum, motor etc.
Hope this helps!