Hi
There is no step by step migration process, depends on your infrastructure, skills,...and the approach you want to use.
I suggest to start with the next links
Knowledge Collection: Migrating to (or from) WebSphere Application Server V7.0 www-01.ibm.com/support/docview.wss?uid=s... Overview of migration, coexistence, and interoperability (in the left frame expand the point)
pic.dhe.ibm.com/infocenter/wasinfo/v7r0/... Migration of WebSphere Deployment from IBM WebSphere Application Server Network Deployment V6 to V7 on AIX 6.1 www.ibm.com/developerworks/aix/library/a... Hope this helps. Tell us if you need more support.
regards