Method # 1 (Individual Pieces)
There are 2 self taping screws holding on the bottom brush section with one screw per each side of the brush once those are removed then they just slide off the bottom of the aluminum core they might of put a couple of self tapping screws in the middle sections as well as on the top, you will notice which ones they are from them not wanting to slide down the aluminum core. Then depending on if the rear arms are equipped with clutches there are 4 - 3/8" bolts holding the aluminum core to the shaft assembly.
Method # 2 (Whole Arm at once)
If no clutches on rear arms you can get a floor jack with a piece of metal or plywood 12" x 12" then use the jack to support the bottom of the brush with the plywood or metal and remove the 4 - 3/8" bolts on the top of the aluminum core attached to the shaft assembly. This also works for the front arms as well.
Also keep track of which brush sections you remove as they are not all the same length if they are the old yellowish cores get a black permanent marker and number each piece on the inside of the section.