To change your modulation type to G.DMT process is as follows:

1.    telnet to the zyxel = click 'start' then 'run' and type 'telnet 192.168.1.1'
2.    login password is the same as the web interface which is 1234
3.    type '24' - to access the system maintenance menu
4.    type '8' - to access the command line
5.    type 'wan adsl opencmd gdmt' - sets the adsl to gdmt.
6.    save, by typing in 'sys save'
7.    exit, then power off the modem and power it back on