Step 3. If upgrading, prepare the current environment (old target system) for the new release

Perform as many z/OS® migration actions as possible on the existing (old) system. These are the preinstallation migration actions that you identified in Step 1, which have a timing of "before installing z/OS V2R1" in z/OS Migration. These migration actions include installing the coexistence and fallback PTFs that you identified in Step 1 and ordered in Step 2.
Reference information: z/OS publications (http://www.ibm.com/eserver/zseries/zos/bkserv/)
Perform as many migration actions as possible for IBM® middleware, IBM applications, and ISV products that run on the existing (old) system. These migration actions were identified in Step 1.
Reference information: IBM product publications and ISV publications.
Build, test, and put the old target system back into production. Follow local procedures.