There is a built in automatic upgrade feature in b2evolution 5.1 and above.
It is generally a good idea to try this before using a more complex form of upgrading. However, as always it is advise that you have made a backup of your site beforehand.
What if auto-upgrade fails and my whole blog is "503 Under maintenance" ?
The "under maintenance" message is displayed because of a temporary _maintenance.html file that can be easily deleted… but this is not what you should do!!
Many times, the only reason this happens is because the upgrade script ran long and got interrupted by your web host. All you need is to restart it, as explained below.
If interrupted (either by timeout or by an error), the upgrade procedure left your blog in a half upgraded state, so you should start by trying to finish the upgrade. In your browser go to your baseurl followed by
/install/index.php?action=auto_upgrade and look very carefully for potential error messages on your screen in order to determine if you just got interrupted because it took too long to upgrade or if there is a more severe problem. Make screenshots for later reference and/or for support in the Forums.
If trying to finish the upgrade repeatedly fails with an error message and no progress between attempts, you will probably need to restore backups. Note that the auto-upgrade procedure starts with making File AND Database backups (see the
_backup folder on your site) and won’t upgrade anything until the backups are complete. So everything should be fixable in a fairly easy way.