Leave it in the sun so the trunk lid gets hot. Stick both fists under the spoiler and start prying it up. Have a buddy standing by to grab it as it pops up. It will come off, just keep constant pressure for a minute or so, then it will pop up.
or you can use a heat gun to warm up the 2X tape. keep pressure on it and use a scraper of some sort. be sure NOT to scratch the paint as you loosen the tape.
I just removed mine to install the roush spoiler a couple days ago. Just grab the spoiler and rock it back and fourth from front to back. It's easier to get it to loosen up from one side at a time then all at once.