Lift one corner of the sticker with a fingernail. If your fingernails are too short, you can use a razor blade.
Peel the sticker away from the case slowly. If you peel too quickly, you will likely tear the sticker. Start peeling in a new corner if the sticker rips.
Scratch off as much sticker residue as possible with your fingernail. Do not use a razor blade for this as it may scratch the case.
Spray WD-40 on any sticker residue you cannot remove. Let it soak into the sticker for one minute and then scrub it away with a paper towel.