Permanently Deleting Lower Level Bookmarks in Adobe Acrobat Standard DC

I have combined 75 files into one pdf. In the bookmark section, I would just like to have the titles of each document that I used to combine to be a bookmark. The lower level bookmarks contain other information from each document.  I know I can "Collapse Top Level Bookmarks". This is exactly how I want it saved. I also see that I can individually delete lower level bookmarks permanently one at a time by using "Expand Top Level Bookmarks" and then "Delete Bookmark" individually. This is very time consuming.

Is there a way to delete the lower level bookmarks all at once? The issue I am having is that when the document is downloaded for viewing by others, all the lower level books are showing up and the viewing document does not have a concise Table of Contents/Bookmark system, but includes all the extra information from the original documents.