Rubber band tool (i use for oil filter also, on my cars, from Sears) i see some people worm up the cap , w/ cigarette lighter, but i never suggest (need to be on open space) .
Make sure to wear gloves that have a grip to them. Tap on the lid a couple of times with plyers or end of a screwdriver, something like that, it should open. Open carefully as sometimes it will slosh out.