Here's what I would do.

Since you used a full version of 6.2.1 Beta Release 1, I would upgrade that board to 6.2.1 Final.

After you get the versions to match, start the restore procedures found at https://www.ubbcentral.com/support/docs/ubbclassic/UBB6_backup_transfer.html

After you get the data moved over, then upgrade to 6.7.1 and you should be in good shape.