Angry [Q] Howto update 41 item pcs of Acer A500 to ICS

Hi all,

I'm newbie in updating android firmware. We have about 41 acer A500, with 3.1 (gingerbread), and want to update all of them to 4 (ICS) official.
I know it just download iconia tab ehnhance from PlayStore + click update.
I just feel update manual of 41 devices is kinda pain with just only 2MB int;l connection.
My POF is save the file in the /cache directory , save to pc, and copy to another tab.
btw i've root all of tab, and familiar with linux command.

1. install terminal > #cp /cache/* /sdcard
arrg whereis the cp command here?

2. install ES File Explorer, copy /cache/* copy to /sdcard
just got a blank folder

3. install cacheDownload2SD
Hoping the cache will appear in /sdcard when the tab download update, nothing happen

I've try coupleof method, not good sor far could someone give enlightment?
Thanks before