If your miner has a failed power supply and you have one to replace it with you should start by removing the top cover from your miner.
Next you should disconnect the power lines from the hashing boards.
After the hash cards are disconnected
You will need to disconnect the power line going to the control card
Once that is disconnected
You can remove the 4 screws on the back of the power supply.
You can the slide the power supply out of the miner.
And then you can replace it with a new one by reversing this procedure.