Updated recently phpBB 3.0.12 to 3.1.8, auto update here does not help, so I will describe the procedure for updating the items:
1) Be sure to make a backup copy of the files and the database of the forum. We will make the standard topic prosilver, disable the rest of the styles and modules, as they will not work on the new version of phpBB.
2) Download the archive with the new version of phpBB from the official site “https://www.phpbb.com/downloads/”.
3) On the server, delete all the files and folders of the forum except the file config.php and directories images, files, store.
4) Unpack the downloaded archive, delete the file config.php and directories images, files, store. Move the rest of the files to the server.
5) In the browser, open the forum address by specifying a database update script, for example http://FORUM/install/database_update.php and following the instructions, perform the update.
At this point, I had an error:
PHP Fatal error: Uncaught exception 'Twig_Error_Loader' with message 'Unable to find template "login_body.html" ... ...
I suspect that the information in the database in the phpbb_migrations table did not allow the script to fully update. So I solved the problem by restoring the old forum base by clearing this phpbb_migrations table via phpMyAdmin or by sql query:
TRUNCATE TABLE phpbb_migrations
And again running the database update script http://FORUM/install/database_update.php, which this time performed the update correctly.
At the end of the update, remove the install directory and clear the cache via the administration panel of the forum. Done.