Hold the brushroll in your hands, and unscrew the ends. One should come off freely, to get the other one out, you may have to tap the shaft of the brushroll with a rubber mallet (on the end where the one cap came off). Then you should be able to hold the shaft with a pliers and unscrew the other end. Everything should come apart from there... Here's the small detail they go into from a Hoover service manual. Remember, the picture below is for agitators pre 1970s or so, that use bearings without the plastic ring attached to the bearing. (It came from a 1960s service manual)
Perhaps, eventually, I could create a "how to" page on this website with a photographic explanation of some very basic maintenance procedures.