I just did this yesterday...
if you connect e0a or e0b to the network, boot off the compact flash and interrupt the boot process
after the LOADER but before ONTAP finishes loading (i.e. when the square box shows up
that says to press control-c to interrupt the boot process)
Then choose the option to install new software.
It will ask which interface and may need to reboot in which case, repeat again
It will also ask for the URL to the software (have the tgz file on a local http server)
and a username (just hit return if not needed)
This should install the latest OS on the boot device and ask to reboot .
FYI, netapp just release a new BIOS/LOADER for the FAS3140 (and a bunch of the newer platforms)
Be sure to update that and if your RLM is less than 4.1, update it to current also.