If an alias is NOT used for the DB2 libraries, change the DB2 library name in PARMLIB(TIRHE) for variable TIRD2LIB. Also change the logon proc, if needed, to allocate the correct libraries to the TSO session. You can check this by logging onto the Host Encyclopedia or z/OS Implementation Toolset, at the Main Menu type TSO ISRDDN and review ISPLLIB allocations for your DB2 SDSNLOAD and SDSNEXIT libraries. There are no special jobs or maintenance that need to be applied to upgrade to a new version of DB2 for the current supported releases of Gen (8.5 / 8.6). The DB2 subsystem id remains the same.
If the upgrade involves changing to a different DB2 catalog DB, then the Host Encyclopedia and/or the z/OS IT will need to be reinstall with new tables along with entering a new configuration (CEINSTAL or ITINSTAL). The models will need to be migrated to the new encyclopedia and new scripts and targets will need to be created for the z/OS IT. Reference the z/OS Installation guide for this process.