Due to some changes in Breadcrumb NavXT 7.3, an update to all of the premium extensions is required before updating to Breadcrumb NavXT 7.3. A selection of premium extensions have already been updated and had separate release announcements (as additional features or bugs were fixed in them). This announcement covers the rest of the premium extensions.
Users with valid and activated license keys should receive an update notification within the WordPress dashboard and be able to use the update mechanism to update (just like with any plugin in the WordPress.org repository). If you run into any issues, please open a support ticket.