If you flip the Dyson DC07 upside down you will see:
If your belt hasn't snapped pull it off the motor shaft
The brushbar can now be pulled out
With the new belt positioned on the new brushroll insert it into the hole and put the brushroll back in place. Than pull the belt over the motor shaft.
Last, replace the soleplate cover and tighten three screws
That is it! It probably took you about 5 mins. and you saved yourself money by doing it yourself. Now save some more money and get your belts at www.vacbelts.com!
Dyson DC07 Replacement Belts