Removing it in cold weather is best...once you have managed to peel a corner up, you will be surprised how easy it is to take off...may rip a few times though but it will come off easier when its cold

Alternatively, you can warm it up significantly so the bitumen is very soft and it will pull away easy...will need to wear gloves and may have to remove some bitumen with a flat blade etc (this is avoided if you take it off when it is cold)