File Manager allows you to edit, delete, upload, download, zip, copy and paste files and folders directly from the WordPress backend. Don’t bother with FTP to manage and move your files from location to location. The most powerful, flexible, and easiest WordPress file management solution ever built!

I hope you solve your problem.

If that isn’t feasible, I suggest you upload the old media into WP, then set up .htaccess redirects so requests for media in the old location can be served from the new location. You can then remove the files from their old location.

Another option on Linux systems if you have terminal access would be to use find and sed commands to search the current files for old path references and update them to the new paths.

All of these require a little bit of coding, but it’s attainable by almost anyone willing to do the necessary research.

Thanks to you too bcworkz for this great piece of advice.
I think I’ll use the redirect method for one folder, which has a lesser number of files.