If you have a support account you can download the firmware from support.arubanetworks.com.
If not, 4.1 has not made it to the cloud as of yet.
I suggest upgrading to 4.0.0.7 and it may give you the option of 4.1, your firmware just may be too old.
Let me see if my IAP with an older firmware gives me the option to upgrade to 4.1