Remove left hand seat. Unplug connections. (Have radio code, unplug battery before disconnecting seat connections or you create airbag lights and have a trip to a dealer to pay for) Undo 4 Torx screws TX50 (3/8). (You can do without this if you are a contortionist and small, just forward the seats and fold the backs )
Remove rear wall lining.
Remove rear wall cover.
Mark running direction with a colored pen. (Better, make a diagram of how the belt runs over the pulleys before you remove it, note which side is down and the direction it goes.)
Turn Tensioning Roller (a/f 24) clockwise and simultaneously remove belt.
Reinstall new belt.
Reinstall hatch, lining, seat.
Connect battery. Reprogram radio if required (later radios don't need a code)