There are sprays that can be used that will kill them, but bumble bees are are pollinators and plants need them to make crops. Since the honey bee population has decreased drastically, bumble bees are needed for pollination.
If you have a real problem with bumble bees and need to kill the bees, make sure you do it after sundown when all the bees are in the nest. Keep lawn mowers and motorized equipment away from the area to keep the bees calm. After the poison is used, the nest must be destroyed to kill eggs and larva.
An alternative to killing them is to contact a professional who might be able to relocate the bees.