The downgrade is the same as the upgrade process. You need a TFTP server that the switch can pull from, you'll need the firmware in the targetted folder that the TFTP server is targetting and you'll need the switch on the network so it can see the TFTP server.
Once you have all that then you...
enable
copy tftp://<IP>/<file name>.bin backup
or
copy tftp://<IP>/<file name>.bin image1 (or image2)
then (and I can't remember the command right now) do something like system boot image1 or system boot backup
then
reload.
I'd have to look at my notes. I keep notes for stuff like this because it's just not possible to remember everything.
But if you can get a TFTP server up and going I'll get you my notes.
Once you have all that then you...
enable
copy tftp://<IP>/<file name>.bin backup
or
copy tftp://<IP>/<file name>.bin image1 (or image2)
then (and I can't remember the command right now) do something like system boot image1 or system boot backup
then
reload.
I'd have to look at my notes. I keep notes for stuff like this because it's just not possible to remember everything.
But if you can get a TFTP server up and going I'll get you my notes.