You can use our app Smart Attachments for Confluence for your purpose.
With its help you can not only edit the attachment name, but also create the multi-level structure of folders, preserve document revisions for change traceability, import folders with files into Confluence with their structure recreation, tag documents with labels for better searchability, and many more.
Feel free to contact me if you have any questions about it.
Welcome to the Community!
Attachments don't have a rename function, that's not what Confluence is for. Renaming a file would break macros and preview functions, so Atlassian have taken the simple route and assumed that you will be attaching files with the correct name that you want, not editing it later.
People have a need to change file names all the time, if I have an attachment which I use in an expand macro, that attachment may need updated multiple times throughout a life cycle. Organizations go through constant change, group name changes, acronym changes, file naming convention changes etc. If product development can't handle evolving with the way people are using the product, then it's time to move on to a new product.
In the attachment macro inserted on a page I see PROPERTIES button where I can change the file name of the file that is already attached. It seems to be out of the box functionality (as works even after disabling all add-ons). Am I missing something or you are talking about something else...?