networking - How to set up modem as a wifi range extender?

I want to use a DSL modem (ASUS DSL-N16) to extend the range of wifi (because of Why do different devices have different wifi reception ranges?).

I read using a DSL modem router as a wifi extender and Can I use a wireless router as a repeater?, and am looking for specific steps.

Is it possible, and how can I do it?