The motor on my contractor's saw is now resting against the stop rather than
completely hanging from the belt. That is wrong isn't it; the belt is
supposed to be holding it up, right?

I presume it has stretched a bit and I have to take a link out. It looks
like you just twist an inside tab and push it through the hole, take a link
out, and reverse. But sometimes thing are more complicated than they look.
So, how do I shorten the belt?

I don't know the brand, but it is red. Thanks.