Nanobds upgrade on 1.2.3-RELEASE
I have installed pfsense on Alix 2d13
"1.2.3-RELEASE Built on Wed Dec 6 11:38:21 p.m. ET 2009
FreeBSD 7.2-RELEASE-p5 i386"
As the time for an upgrade can I reflash with the appropriate sized nanobsd release for my CF card "pfSense-2.0.1-RELEASE-i386-4g-nanobsd-upgrade.img.gz"
You can download that upgrade.img.gz file and apply it from System > Firmware.
That upgrade image would not require a "reflash" from 1.2.3 there, it upgrades in-place via the GUI (or console update), and retains your configuration.
If you want to wipe the card and reflash starting with 2.0.1 you would need the full image (it does not say upgrade in the filename), and that would not keep your config you'd have to take a backup before starting, and then restore that config backup after booting the newly imaged card.