There is a built in automatic upgrade feature in recent versions of b2evolution.

However this is still experimental and we still encounter some bugs here. (Did you see the red warning?)

Thus, at this point we still recommend you use the Standard Upgrade Procedure until this has proven to be rock solid.

Note: we especially do not recommend attempting the auto upgrade if your currently installed version is below version 5.0.9-stable. This is not a guarantee that everything will necessarily work after version 5.0.9 but it’s much stronger than it used to be (especially on low memory systems).

What if auto-upgrade fails and my whole blog is "Under maintenance" ?

The "under maintenance" message is displayed because of a temporary _maintenance.html file that can be easily deleted.

However, if the upgrade procedure left your blog in a half upgraded state, you will probably need to restore backups. Note that the auto-upgrade procedure starts with making backups (see the _backup folder on your site) and won’t change anything until the backups are complete. So everything should be fixable in a fairly easy way.