This video from ANS Gear on the EMC kit does a good job of explaining how to take everything off of the old body.
You will be keeping the feedneck and potentially eye covers depending on which body you purchase.
Note: In the video he shows some strong resistance to taking the body off, but so far every customer as remarked that they have had an easy time of removing the body. Our experience has been an easy slide off as well. Please note that the tube bodies do tend to be a bit more snug.
Order of installation:
Insert inner body
Assemble on trigger frame
Attach eye/detent covers (be sure to do this after assembling the body to the trigger frame)
Troubleshooting note: If eye covers do not go in smoothly, make sure that the marker outer body is fully seated on the inner body.
This video shows how to exchange the POPS ASA bonnet. We found that using a lever to pry open the ends of the bonnet helps immensely but be sure to use plastic when doing so to prevent damage to your ASA.