Steps to upgrade vbulletin is similar to the installation process, there may be special requirements for upgrading vbulletin from different versions, especially if your vbulletin version is much older than the current release. You should double check the upgrade process for your current version before proceeding.
Prepare for upgrade
Nothing is more important than backup mysql database and vbulletin program folder, you must have a working backup so that in case there is anything wrong in the upgrade, you have the option to restore your forum to a previous working condition. Please do take note that in an upgrade process, files are overwritten and database is modified, and these changes are permanent, if there is anything wrong during upgrade, the only option is to restore from a working condition backup.
Before making any backups, you should also turn off your forum from visitors to avoid new data not being captured in the backup, as well as ensuring a smooth upgrade process, do note that there will be changes made to database schema, and you should ensure there is no one except the upgrade program is accessing the database.
Preparing new vbulletin files
Login to the vbulletin members area with your Customer number (not the license number) and download the latest stable release of vbulletin program. Uncompress the file in your computer and rename the upload folder to the folder name of the vbulletin program folder currently in your hosting account. For example, if your vbulletin program folder is named forum in your hosting account, rename the expanded upload folder name in your computer to forum.
Remove the install/install.php file in the renamed forum folder, you will not need this file in the upgrade process.
Upload the newly renamed forum folder to your hosting account, and overwrite the files in the forum in your hosting account.
Running the upgrade script
After replacing all the files, you can start running the upgrade.php script, open up your browser window and enter the url to the the install/upgrade.php script, for example http://www.yourdomain.com/forum/install/upgrade.php. In the first screen, enter your Customer Number and click Enter Upgrade System . There are several steps depending on the current version and the target version, there is generally no action required on your end except to read through the messages on screen and click Next Step after reading each screen.
IMPORTANT NOTE: Do not refresh your browser window in any of these screens, otherwise the backend process will be making double changes to your vbulletin program and database, and the vbulletin will not be function properly after the upgrade, you will likely need to restore from your backup and go through the upgrade process again.
After the upgrade process, you will be automatically redirected to the Admin Control Panel login page.
Check through your new vbulletin setup
You should double check through all the setup before turning on the forum to your visitors, especially if you have made changes to the default template, you will need to apply the changes again manually.