Your brake light switch is located far up on the brake pedal. You need to get your head right next to the floor to look up and see it. You will need to take the plastic panel off from under your steering wheel to get to it. It is difficult to reach but fairly simple to replace.
There are two types of switches, depending on whether or not you have cruise control. Make sure you buy the correct type. The switch is also adjustable. If you think your switch is not working, trouble shoot it by pushing it manually with your finger while someone else checks your brake lights.
I've also had the switch fail where it is stuck in the on position. This will burn out all your brake lights. You may need to change your brake lights after you replace a bad switch.