How to change the serpentine belt?
 

I have a 2011 Honda Fit Sport and the video walkthroughs online aren't helpful. They don't have the same system I have. I really don't want to take it into a shop to have it done. I'd much rather just buy the tools I need. I have a basic ratchet set, but to take off that huge bolt on the alternator is going to be a bitch. I don't know which tool I need to take it off, or how big it is.

Also, how do you adjust the tension on the belt?

I wish I could help Sonnington, but I have the exact same question as you have. Most of the videos and explanations are for the earlier generation, not our GEs and the set up is different as you found.

It seems that the Tensioner is not provided with the usual 3/8" Square socket, but instead with a 19mm Hex Head socket. The inside of the bolt where the 3/8" square is usually found is merely an indented round well. :-(

Literally found in 2 seconds on google

They are looking for 09-13 Fits...

Put a 19mm wrench on the hex and turn it counter-clockwise to loosen tension on the belt and pull the belt off.
https://cimg9.ibsrv.net/gimg/www.fit...4be41e83ed.jpg