Terminology! Jailbreaking applies to Apple devices. Rooting is what happens to Android devices.
There are dozens of utilities in the Play Store (silly name, I know) but my programme of choice is KingoRoot. You doenload it into a Windows machine and connect the device via USB.
Some manufacturers and even some Service Providers, prevent the rooting process so don't be too surprised if Kingo can;t complete teh job.
Before you start, go into Settings :About Device. Tap on Build Number seven times and you'll see "you are now a Developer". Back in Settings there's a new category - Developer Options. In there, enable USB de-bugging or you can't successfully connect to a PC by USB cable.