There is a spring loaded tensioner built into the idler pulley.
Step 1 = work out the routing
Step 2 = Using a socket, slacken the tensioner
Step 3 = Remove old belt keeping the routing in mind.
Step 4 = Fit new belt
Step 5 = Release tensioner
Step 6 = Sit back and admire your work
Takes less than 2 minutes = if you can find the right socket.
Somewhere on TM IIRC there are pictures but once you try the idler with a socket it all becomes very clear.
New belt is Gates 6PK1203
