ZyXEL routers. How do I change its MTU?

Telnet to the Router by doing this:

Go to Start/Run... then type telnet 192.168.0.1 and click OK button. Now enter your password... (the original is 1234). You will get a menu.

Go to menu 24.8 (type 24 Enter 8 Enter). This brings command line interface. At command prompt type the following command followed by Enter:

ip adj wanif0 1300

This will lower the current MTU limit to 1300.