1. From the management switch, copy the firmware to other stack units using this command :
Switch(su)->set switch copy-fw destination-system <Unit-NUMBER>
2. Upgraded Unit requires a reboot in order to run the newly copied image and allowing it to join the stack.
Note: C5 or B5 Firmware version 06.42.xx and lower cannot talk to switches on 06.51.xx / 06.61.xx or higher due to 06.42.xx code track has different programming for stack port intercommunication. Any C5 or B5 on 06.42.xx should be manually upgraded prior to joining to a stack as the above commands will not work