This is from the latest 11.0 release notes:
5.5 Upgrade Instructions for Server Edition and Applications Server
If using a DVD to install this release of IP Office Server Edition and Applications Server,
you can upgrade directly from the previous GA release (10.0 or 10.1) For further
information, please refer to the “IP Office Application Server 10.0 Installation and
Maintenance” and the “Upgrading” section of the “Deploying IP Office Server Edition
Solution” manual available from the IP Office Knowledgebase. Upgrades are
supported from the latest service packs of 10.0, 10.1 and 11.0.