How to replace side mirror glass?

[CraigH]

I've just broken my mates L/H mirror glass on his 07 FL 2. I picked up a new genuine LR glass assembly today, which has the backing on it. It looks like a simple case of popping the old one out and snapping the new one in but since I've done enough damage today I want to be sure how to go about replacing the glass without causing more Damage.

Any ideas on how the correct procudure?

Cheers
Craig