How can I gain access via ftp to the root of my server? I can only access the domain-names that I created.


I must say that, accessing root (/) of your server through ftp is not a good idea, regarding security issues,
anyway, if you wish to add such ftp account, that goes into root or any dir do as follows:
* there is no automatic way, in ehcp gui, so, you will do a bit manual,
* go to phpmyadmin, go to ehcp db, ftpaccounts table, append a user with home dir or you wish, as similar to other records...
* go to ehcp gui, just append a random ftp accuont and delete it.. (This syncronizes ehcp db to filesystem, hence adding actual ftp that you added in previous step..)

That should do what you want..

this don't give full access... only reading files

in console:
chown -Rf vsftpd /path/to/yourfiles/inftp

this will give full access in ftp, manually,
for new user add in ftp, in ehcp, no need to do this.
only in case you need it exclusively

Another easy way, with at least some security is to use sftp.
Install openssh on your server, and use a ftp client capable of using sftp. (filezilla does the trick)

Yes, i agree
your server should already have ssh access.
So, obtain filezilla client, then choose sftp as connection type, then connect using filezilla, with your root pass. without any setting in ehcp..