Hi. What does the burning smell of? Is it 'rubbery', or is it acrid and 'chemically'?! The most common item to 'burn' is the belt which drives the rotating brush at the front. Does your cleaner have a belt? This would give a burning rubber smell.
The instructions should explain how to change the belt - have a close look and see if the belt has been slipping on the motor spindle. If it has, then it'll probably be worn at this point and should be replaced. A common cause of this happening is the brush bar getting caught in something - edge or rug, etc - and being forced to a standstill.
If the smell is more 'acrid', it could be a problem with the motor. This is a repair service job.