Sorry, for some reason I didnt see the "Upright DC07" bit!
Below the on off switch on the front of the machine is a small silver torx screw, this needs to be removed. Torx bits/screwdriver sets can be bought a most DIY shops. If you're lucky enough to have a small flat bladed screwdriver (Like me) that fits perfectly into the screw then use that.
Ensuring the machine is not plugged in, remove the screw and the plastic housing from the switch mount. You will need to unclip the clips behind the housing from the rear of the machine.
Once you have access to the wiring, write down which colour goes to which, disconnect both wires and remove.
Fitting the new wire is the reverse of this process, re-fitting the housing is quite difficult/awkward but persevere and you're done.
Take note of the way the cable is routed behind the hosing when you remove it. Replicating this arrangement will help you replace it.
Stu, November 2007