To have a better understanding of Vietnam Airlines' upgrade policy and the procedures involved. You'll need to go to the official website for further information for HOW DO I UPGRADE MY TICKET AT VIETNAM AIRLINES?
www.vietnamairlines.com is the official website's URL. It is critical that you copy the URL accurately since you will not be able to complete the upgrade without it.
You should keep in mind that upgrades are only granted to passengers. Those who have made reservations on this official website.
If you booked your flight through a travel agency, you will not be eligible for an upgrade.