What's the model?
Can use Utility to do this:
Go this link and download the tpPLC utility for MAC : http://www.tp-link.com/en/download/TL-WPA4220.html#Utility
On the utility, move the mouse to the unit and click on the Global icon then you can log into the interface of the device. Then you can go to Wireless section and change wifi settings.

Thank flying snow,
I found this solution also and it works.
Topic can be closed.

René

Thank you flying snow,

I found it too, it works.

Topic can be closed.

Rene