Not sure if you've removed the side cover to remove the roller assembly or not. If not you will need to do that prior to lifting the top cover off as there are levers attached to the cover. I've attached some pics, if you don't have a manual I'd suggest you either get one or visit your local dealer, they'll have a shop manual and most are willing to help you.
Don't try removing it if you haven't removed the roller assembly, the levers are stout but can be bent if enough force is applied.