Install (or rollback) to previous version of OS

No need to ask why I need to do this, trust me I need to do this.



I have a Power 8 with 4 partitions.

All partitions are currently running 7.2

Currently in the process of updating one partition to 7.3

Want to update one partition back to 7.1 (not even sure if this is
called update? rollback? downgrade?)



At one point in the past I had CD's for 7.1 but can't find them now.

I am under SWMA so I can get 7.1 from IBM (download from IBM web site,
can't find a way to order 7.1 CD's).



My question is: What is the easiest way for me to install 7.1 on one
of the partitions running 7.2?



Thanks in advance for any suggestions or advice



John