Moving Upstream Pro to other wifi network

I have installed more than 5 Upstream pro boards in hifi installations of friends. I have found that when I have tested any of those on my own wifi network it works fine. However sofar it was for me not possible to get it working on the wifi of the end user. Only with network cable will it work again. This is quite a nuisance. What should I do to make it forget the first wifi network and password and have it connected to a new wifi network of the end-user. Thanks for your answer

Have you tried pressing the reset button? This should clear the stored network information.