conversion of a normal modem into an Wifi-modem?

I have bought a modem 6 years back. That modem is of normal kind and doesn’t have any Wifi settings in it.But recently Wifi-modems gained wide popularity.My modem is still in a good condition. So I don’t want to replace it with a one having wifi settings. I need to know whether there is any option to convert my modem into a wifi modem? If it is possible ,what are the steps i need to take to get wifi settings in my modem?