Open your Sugarbook app. Tap the menu icon (three-line icon) at the top left of the screen. Tap on Edit Profile followed by Photos. Tap on any public photo you wish to set as your main photo. At the top right of the screen, tap on "Set Profile Picture".
Log in to your Sugarbook account. Click on your profile icon at the top right of the browser followed by Edit Profile, followed by Photos. Click on the gear icon on any of your photos and select Profile Photo.