Word of advice, just start now spraying them down with PB blaster. Give yourself the best chance to break them out cleanly.
Toyota wants you to remove the headers and mid pipes from the truck, then remove the sensors. When I used to work at a Toyota, I always tried to get the O2 and air/fuel sensor out without removing headers and mid pipes, but about half the time, i just had to. the sensor required too much force to break free.
Also to help your pocket book, Denso builds the sensors. If you want the good OE part for cheaper. Go to the Denso website and pull up the part number. Then go onto amazon and order 2x "Denso 234-9026" (that's your air/fuel or upstream sensors) for $100 each and 2x "Denso 234-4169" (that's your O2 or downstream sensors) for $40 each.
Through Toyota the air/fuel are $140 and the O2 are $120, that will save you $240 on the exact same product. Literally the exact same, just doesn't have a "Toyota" on the box, but that doesn't matter, because they are really Denso.
Torque all sensors to 32 ft lbs