Uberflip does not have a feature to insert and delete pages in your Flipbook.
Our system was not built to accommodate that kind of feature. A major rebuild would be required to support inserting and deleting Flipbook pages.
We will not be looking at building that feature for the foreseeable future; however, we do have the option of replacing a page of your Flipbook with a new one.
We thank you for your understanding and please be sure that your PDF is finalized in the number of pages prior to upload.