Clear password:

enable
set password enable clear
set password exec clear

Erase current configuration:

enable
set nvram erase
write
reboot

Set bridging mode:

enable	
set bridging rfc1483 enable
write
reboot

Set PPP mode:

enable

set password enable <enable-password>
set password exec <exec-password>

set ppp wan0-0 ipcp 0.0.0.0
set ppp wan0-0 dns 0.0.0.0
set ppp wan0-0 login <ppp-user-id>
set ppp wan0-0 password <ppp-password>
set ppp restart enabled

set int vip0 ip <gateway/router-ip-address>
set int vip0 mask 255.255.255.248

set nat enable

Turn off Web server:

set web disabled
set web port 6666
set web remote <remote-ip>

Turn on TFTP server:

set tftp enabled
set tftp remote <remote-ip>

Enable DHCP server (optional):

set dhcp server enable

Save new configuration:

write
reboot