Change onedrive accounts

Another paid product option to consider: cloudHQ Sync and Backup (www.cloudhq.net) which does server-to-server endpoint sync/migration/backup. You basically tell it the endpoints you want to connect to (in your case, each OneDrive account), the type of sync (direction, bidirectional, one-time-move, etc.) and it takes over from there with good quality reporting of events. I've been using them for about a year now on a number of projects and it works very well for this scenario. It's $50US/month, but they also have a free plan - no idea what it's limits or capabilities are though. It's more than paid for itself several times over for me and their support has been excellent.

Bob

If you have the space, your best, and probably easiest way is to sync both accounts to your PC. Move the files over, let it sync up done. But this would require a 2+TB free disk space.

Other ways could be to use explorer view to move the files from one to the other but you'll want to do them in smaller batches incase there are issues during move.You can access that by using Internet Explorer and in the view drop down in the top right is open in explorer, navigate to both onedrives in IE and open these, then you will have both open you can drag and drop files between them. Again, Do in smaller batches by folder(s).

Another option is using a migration tool such as the SharePoint migration tool, but I'm not 100% sure that can go onedrive to onedrive, so probably not best option to mess with :P