Here is what is needed if you are starting with a 16" barrel upper. I you have a 20", you will need a 16" gas tube.
Barrel, float tube, gas block or sight to fit the new larger barrel.
Upper vise block(plus vise)
Barrel wrench( with torque wrench)
punch(for gas tube roll pin)
Band tool
Start off by pulling the hand guards, then clamp the upper in a upper vise block.
Punch the gas tube roll pin out, then pull the gas tube.
Using a barrel wrench, spin the barrel nut counter-clock wise to remove the nut.
Pull the barrel straight out, do not twist.
Install the bull barrel in the receiver, then use the inner float tube nut to tighten the barrel to the receiver. You will tighten the nut three times to 35 lbs on greased threads, then on the third time, once you achieve the 35 lbs, turn the nut a little more to aline the top nut hole to the receiver gas tube passage.
Using a band tool, install the tube to the barrel nut and tighten.
Install the old gas tube to the new gas block, then make a pencil mark on the barrel(at the barrel shoulder to show gas port location) to aline the block gas port to the barrel gas port. Insert the gas tube and gas block on the barrel, then insert the gas tube threw the nut/receiver gas tube passage.
once the block is aligned to the pencil line(port to port) , tighten the bottom screws on the gas block.
Pull the upper from the block and re-insert it back on the lower.
Drop a head space gauge in the chamber and check to see that the head space is correct.
Your done.
Total time 4 minutes, including time to drink a Pepsi.