Hey, you can boot into the older firmware by changing the controller to boot in the partition you required. For example if you look at the output below, we can see there is 2x partitions each with a different version.
(001) #show image version
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Partition : 0:0 (/dev/mtdblock9) **Default boot**
Software Version : ArubaOS 6.4.2.5 (Digitally Signed - Production Build)
Build number : 48774
Label : 48774
Built on : Tue Feb 24 22:02:57 PST 2015
----------------------------------
Partition : 0:1 (/dev/mtdblock10)
Software Version : ArubaOS 6.1.3.4 (Digitally Signed - Production Build)
Build number : 34587
Label : 34587
Built on : Mon Jul 23 15:48:34 PDT 2012
We can see that the controller is running currently from partition 0:0 as this has the **Default boot** next to it.
If you wish to boot into the other partition, change the boot statement 0:1
#boot system partition 1
And then review the output of
#show image version
Once you are happy for the controller to boot from the required partition then simply reboot the controller using the #reload command