Constant Content

I revised an article and what's visible to me are 1) Previous Submission and Reattach File 2) Attached Files and 3) Add a New File. I chose Add a New File. First, I deleted the old file from the Content Text box. Then I copied and pasted and choose a New File and Uploaded it. My revision is not in the Content Box even though it was uploaded it as a New File. I can't seem to get rid of the old text. My previous submission is in the Content Box even after I delete it.

Any idea what could be going wrong here? Copy and paste never works smoothly for me. How do I get the revision in the Content Box? Shouldn't I just be able to copy and paste? When do I use Reattach File? I just want to see if there is any author help for me on my Mac OS before I contact technical support.