How to change Keras backend (where’s the json file)?

Question

After looking at keras sources (this place):

Start up your python-binary and do the following

import os
print(os.path.expanduser('~'))
# >>> C:\\Users\\Sascha'  # will look different for different OS

This should be the base-directory
Keras will build an folder .keras there where keras.json resides (if it was already created). If it’s not there, create it there
Example: C:\\Users\\Sascha\\.keras\\keras.json'