Turn the product over and remove the brush locking bar - Use a small flat blade screwdriver twist the locking screw anti clockwise remove the bar and lift out the brush as shown:

To remove the belt it is necessary to take the top cover off. Remove the 8 screws around the lover casing 2 of which are hidden behind the little front rollers. Prize out the 2 little wheels to get to the screw as shown:

note the belt shown here connected to the silver motor on the left of the picture

Remove the broken or worn belt and replace with a new belt.