My apologies. Indeed I have not worked on this case before, and I assumed that it's like most other cases. Pardon my ignorance.
I have taken a look at the instruction manual now. I hope to be able to assist you in this.
From my understanding, the half frame that you are referring to, is the PSU mounting bracket. You would first have to remove the bracket by removing any screws that hold on to it right now. From the illustration, it would seem like 2 screws from each side are holding on to the frame.
After removal, proceed to mount the mounting bracket to the PSU. Instructions will be the same as with my first answer, but not to the case, as you are securing it against the bracket.
After which, put the PSU with the mounting bracket installed back into the case. Plug the case's power cord into the PSU and slide the PSU back in. Now, rescrew in the mounting bracket to the case. Same spots to where you remove the bracket. The PSU should be successfully installed right now.
I sincerely hope this helps. Hope to hear back good news from you.