Is it possible to move a account with his database from cPanel to HELM and how !?!...

The two systems are very different--I know because I use both. I am not aware of any automated transfers between the two.

My approach would be as follows:
* Start with the daily Cpanel backup archive and unpack it somewhere, e.g. your Helm server.
* Copy the contents of public_html to the relevant wwwroot folder.
* If there is a MySQL database involved, create a new one in Helm, and then import it using the mysql command line tool.
* Manually recreate mailboxes and forwarders in Helm.
* Update the name servers to point to the new IP on the Helm server

I hope this helps

Thanks, Stefaans; I will do a try...