changing the image cover of the cliente interface

hello,
We are in need of chaning the cover that we are using for the client interface (where they introduce the password to log in to the wifi), could you please let us know where do we have to go to change this?

Thank you
Regards
Benjamin

Dear sir

If you refer to the password setting of the new Cloud you can refer to this pic:

if you referred to the password of wifi, you can refer to this pic:


Best regards，
Ross