How to set the ringtone for incoming calls on your iPhone is as follows:

1. Set the system’s own ringtone

Open the “Settings” application.

Scroll down and select "Sound & Touch." On the next screen, you will see several tabs including "Ringtones", "Alerts", "Notifications", etc. Select the "Ringtones" tab. You will see a list of ringtones that come with your system. Browse and select your favorite ringtone and click on it. You'll be taken to the next screen where you can adjust the ringtone's volume and vibration pattern. When finished, click the "Back" button in the upper left corner. You have now successfully set the system's built-in ringtone as the incoming call ringtone.

2. Set a custom ringtone

First, you need to add your favorite songs or audio files to your iPhone. This can be done through iTunes or other third-party applications. Open the Settings app. Scroll down and select "Sound & Touch."

Select the "Ringtones" tab.

At the top of the screen, you will see an option called "Select a song." Click on it. You will now be taken to the Songs screen, where you can browse and select the song or audio file you just added to your iPhone. Select the song you want and click on it. Adjust the ringtone volume and vibration mode, then tap the "Back" button in the upper left corner. You have now successfully set a custom ringtone as your incoming call ringtone.