How do you replace the front O2 sensors on a 2001 Toyota Sequoia?

Unscrew them and put in new ones. They can be very difficult to remove, as they tend to become frozen in place and are difficult to access. I tried to get Bank 2 Sensor 1 out and it was hopelessly frozen in place and very difficult to access. I will try penetrating lubricant from Kano labs, as suggested on a website. WD 40 and Parts Blaster were worthless.