To change the watch facefrom your watch:
Long press on the current watch face of your watch.
Slide your finger from right to left on the screen to scroll through the available watch faces.
Select your favourite watch face by tapping on the one you wish.
To change the watch face from the MyKronoz app:
Go to the watch face tab (located at the bottom right of the screen) of the mobile application.
Click Select watch face.
Select the watch face of your choice by tapping on it.