Follow the cable from the hub until you come to a connector, it looks like a lump on the cable , this pulls apart but can take quite a strong pull and a bit of wiggling to separate the two parts. When you have this unplugged the wheel nut can be undone and slipped over the cable to allow the wheel to be removed. When re- plugging the connector look for arrows moulded in to each part of the connector. These arrows should be lined up with each other before pushing the connector together. If there are no arrows, look at the pins carefully and the matching sockets , the correct alignment will be obvious. Take your time and a squirt of Wd 40 will help things along. Make sure everything is switched off or take out the battery while working on unfamiliar electrics. Putting an ink spot on each part of connectors will help you keep them right. If you are still having problems,post a pic for more help.