How to use PTCL AN1020-25 routers/modem as just a modem?

How can I use PTCL AN1020-25 routers/modem as just a modem ? Basically I want to use a better router (Linksys E1200) and install dd-wrt on it and use the PTCL AN1020-25 routers/modem to provide internet access to the devices connected to the new router.Hope I'm making sense.

U want to turn off old modem wifi?

And want to connect it just to the new modem right?

If PTCL DSL Router is already attached to your PC then open brower and type IP to login router administration.

Go to Wireless and Unckeck Enable Wireless.

Click [Apply / Save]

Go to LAN and Modify IP Addresses.

IP Address:

[Enable DHCP Server]

Start IP Address:

End IP Address:

Click [Apply / Save]

Click [Reboot] to restart router.

Once complete verify that wifi signal is off and then connect your devices in this manner.