It is a wasps nest, Is it very near the house or any areas people frequent? Wasps are important pollinators, so you don't want to kill them unless you have to. If you need to, as winter is coming, you can wait until winter sets in, then cut the branch the nest is on, and drop it into a bag or box - they are cold-blooded, so dormant in freezing temperatures - then you can bring it to someplace else - woods or somewhere unihabited, and dump it out. If it needs killing, you can buy spray to do so, but do it early or late in the day when temperatures are coolest, so the wasps will be less active. They are fiercely territorial, so you want to catch them at their most sluggish, and when most everyone is in the nest.