This was tested for Oqtane v3.1+ and works without issues.

Important: This will not work with Oqtane Source code version.

Pre-Requisites

1. You have Oqtane installed as a release-build (not in dev-mode) and a host account
2. Ensure you created backup of your web folder and sql database.

Automatic Upgrade using System Update

1. Login as host user and open Admin Dashboard / System Update
   
2. If Oqtane Framewrok is not already up to date, you can select the [Download] button to download the framework upgrade package and then select upgrade.
   
3. After several minutes, you can log in and check in Admin Dashboard / System Info that Oqtane version is upgraded.
   
   
   

Alternative: Manual Upgrade

1. Copy the wwwroot/app_offline.bak to the root folder and rename it to app_offline.htm. Your website should now be offline (please verify)
2. Now get the Oqtane zip file and unzip everything into the root folder, overwriting all DLLs and everything
3. Delete your app_offline.htm and visit your site again, everything should be upgraded

Install 2sxc

This is optional, but most Oqtane installations will also want to install 2sxc or upgrade 2sxc.