I have just succesfully completed this task and have found that you will need the following equipment.
1) Sharp Knife
2) Sturdy pair of garden seccoteurs
3) Some semtex
It took me approximately 30 mins to get the old one off using a combination of hacking it to bits with the sharp knife and then slicing it with the seccoteurs... by the time you have finished the old one will be it about 10 thousand bits and you will feel like you have been in a fight.
Enjoy.