Desktop: To change your password, click "Bonjour" at the top right and choose "My Profile". This will open your account information where you can enter a new password.
If you forgot your password, simply navigate to https://app.opsi.io and click "Forgot Password" at the bottom. Follow the instructions to reset your password.
Mobile: To change your password on mobile, tap "My Profile" icon in the main navigation. When in My Profile, tap "Settings" then "Edit Account". Within this Edit Account view you can update your password.