To change the ringtone:

1. Go to the Settings icon
2. Scroll down to Sound and tap it
3. Tap Phone ringtone
4. Select a ringtone of your liking. Tap on it to listen to it, it will play once
5. Press OK at the bottom to confirm your selection.

You have successfully changed the ringtone!

If you want, you can also scroll all the way done to add a ringtone of your choice.