Remove the 18 screws. eject the optical drive with a paperclip, and then pull the whole thing straight out. It may not want to come, but it will come, you are sliding it out of a SATA connector. It is not screwed in to anything (as long as you removed ALL 18 screws.)

After optical drive is out, remove three more screws now visible/accessible in the optical drive opening.

If you start at the optical drive end, it will probably be easier than it was for me (I thought the optical drive was still bolted in, and had to half remove cover before freeing it.)

I struggled to get the cover "over" the usb & other ports, but if you start from the other end, it may be easier.