I’ve dealt with this numerous times over the years. The rotating beater bar is designed for easy service on practically any vacuum. Sometimes things just snap apart & sometimes you take out a few obvious screws holding a plate over the ends of the bar to get to it.
Once you remove the plate the bar should lift right out of the machine (though it may still be attached by the belt) and the end caps over the bearings removed in order to clean out the hairs and threads wrapped around the bar & bearings. Here’s where you’d put in a new belt, if necessary, then reassemble.
In tough cases it takes a while to clean & you might have to resort to cutting across tightly wound-up threads with a razor blade or knife to remove them
If you ever smell burning rubber, it’s the belt & you should immediately shut the vacuum down until you get the beater bar freely rotating again. On a shag rug it’s possible the beater bar simply jammed after sucking up a fold of rug, without actually being gummed up with fibers. The lesson: When using the wand you should put the vacuum on a hard floor or set it on its back so the bar can’t jam.