You can upgrade to CollabNet TeamForge from CollabNet TeamForge 5.3, patch 2.
To upgrade from any version older than 5.3 (including CollabNet SourceForge Enterprise 5.x or any version of SourceForge Enterprise Edition) first upgrade your site to CollabNet TeamForge 5.3 and start it up. Then follow the steps for upgrading to CollabNet TeamForge 5.4.