Thread:Project:Support desk/Upgrade 1.4.12- current/reply

See Manual:Upgrading. However, one step of the procedure should be stressed in that case: UPGRADE EVERYTHING.

In simple words: php maintenance/upgrade1_5.php --upgrade php maintenance/upgrade.php
 * 1) Backup
 * 2) Upload new files
 * 3) In command line:

I'm not sure about upgrade1_5, things may work without it.