The only thing needed is to turn off write cache.
There are two sps's at the bottom of the DPE chassis. One of them will likely have an amber light indicating that it is faulted. Replacing the SPS requires you to unplug the ac input to the defective sps.
So, I would suggest you make doubly sure that the ac plugs on the good sps are in good and tight before you start to remove the faulted unit. (particularly if you're doing this on a live system).
Remove two screws in the front of the unit for the failed sps and then the screws that attach it to the rear.
Unplug the ac cords on the failed sps only. You will get a power supply fault and a fan fault because you are removing ac to one of the power supplies.
Unplug the RJ45 SPS monitoring plug.
Slide the unit out.
Reverse the process to put in the new one.
Once you power up the new sps and reconnect the monitor, the Storage Processor will test it. So, you'll see an amber light for awhile and it may take a bit of time to recharge.