How do I unplug the battery?

Use a 10mm spanner and remove the positive lead mate. That should do it.

Or the Earth Terminal lead, less risk of a direct short and sparks when the spanner slips and grounds!!!!

When you reconnect a number of warning lights will light up on the dash, from memory these are ABS, ESP
and a few others. A very short drive (yards) will remove them, you may have to reset the tyre pressure monitor
if you have it.