If you want to change the ringtone on your iPhone, follow these instructions:
Step 1 – On the iPhone's home screen, select the Settings app.
Step 2 - In Settings, select Sounds.
Step 3 - In Sounds, move down to the Sounds and Vibration Patterns section. In this section, look for Ringtone. That displays what you currently have as your iPhone ringtone. Tap here to change that.