Unplug the vacuum cleaner.
Remove the cover to your vacuum cleaner, using a screwdriver. Check your vacuum cleaner's owner's manual to make sure you remove the cover properly. If you've lost your owner's manual, most manufacturers make the manuals available in .pdf format on their websites.
Remove the old belt, and install the new belt either according to the directions on the package or according to your owner's manual.
Replace the cover and plug in the vacuum cleaner. Turn it on and examine the vacuum to make sure the belt is no longer slipping, causing the burned rubber smell. If the belt is still rubbing, you may need to take your vacuum cleaner in for service.
Sprinkle a small amount of baking soda onto a patch of carpet. Use the vacuum cleaner to clean up the baking soda. As it moves through the vacuum cleaner, the baking soda will deodorize the remaining burnt rubber smell. Leave the baking soda in the vacuum cleaner's canister for continued deodorizing until the next time you vacuum.