Paper won't feed. Mechanical failure

I have an HP OfficeJet 6500 AIO E709A all-in-one printer. The "out of paper" warning appears..., ...paper won't feed..., etc. The problem is not software. There is a small arm with two ribbed rollers that drops on the paper tray and feeds the paper. Those rollers are not turning. It could be easily repaired if I knew how to get the darned top off the machine. Any one able to help?