Beater bar belt needs replacedon a dyson DC14 animal

Remove the glide plate at the bottom of rhe machine. Remove brush and broken belt. Fit new belt and re install brush. Fit glide plate, job done.
Its in the instruction book

If your Dyson is more than 3 years old and the drive belt is still attached to your brush roll, The most likely cause is a stretched belt slipping on the clutch. your brush roll encounters friction on the carpet and if there is not sufficient tension in the drive belts, you have 2 of them, then they will slip and you cannot pick up debri as the vacuum was designed. You have a few options, call the Dyson help line located on your vacuum via a sticker behind your hose; explain to them the problem with the brush roll not turning sufficiently. There are also replacement belts available for your model at a cost of around $10 depending on your area, but you have to take the clutch assembly apart to install the new belts. Lastly you can buy a new clutch assembly for about $70 but this is a last resort idea. Any reputable service center should be able to replace a clutch in 5 min. and rebuild one in less than 20 min.
Hope this helps.