Start at the top, just on the bend or where it meets the door card, use a small flat screwdriver and a cloth to protect the plastic, prise it off,once one clip has released you can just pull the rest of the trim out by working your way down. At the bottom end it has a hook so once it looks like it's free you need to slide the trim towards the front of then car to remove completely.
When you have removed it you will see the clips and hook, which will make taking the other one off and refitting easier.
Star! Lesson learnt - if its not giving way at one end, try the other!
I was wondering why it was still hanging on when i tried it from the bottom! managed to get them off easily now, although inevitably my screwdriver slipped at first attempt and now theres a minor scratch