WebSphere Partner Gateway 6.2.1 is a refresh pack of V6.2. This pak file is installed on the top of V6.2 using IBM Update installer (UPDI). With the release of WebSphere Partner Gateway v6.2.1, migration to WebSphere Application Server v7.0 is supported. A very frequently asked question is if its mandatory to be on WebSphere Application Server v7.0 to operate WebSphere Partner Gateway v6.2.1.
Migrating WebSphere Partner Gateway V6.2.1 profiles on WebSphere Application Server V7.0 ND is optional.
For actual steps to migrate , you can follow the below link :