This page has the update and testing instructions for the current ITB 1.1.31 (OSG 1.2.19 candidate) update.
If you are updating from version 1.1.21 or earlier, you need to do a fresh installation. This is because the ITB cache changed locations to a different server.
If you are updating from version 1.1.22 - 1.1.25 see these update instructions
If you are updating from version 1.1.26 or later see these update instructions