Find and download the desired free ringtone to your computer. You can use websites like Zedge or Mobile9 to browse and download free ringtones. Alternatively, you can create your own custom ringtone using software like iTunes or GarageBand.
Connect your iPhone to your computer using a USB cable.
Open iTunes on your computer. If you don't have iTunes installed, you can download it from the Apple website.
In iTunes, click on the device icon located in the upper-left corner of the iTunes window. This will open the summary page of your iPhone.
From the left-hand sidebar in iTunes, click on "Tones" under your device name.
Drag and drop the downloaded ringtone file from your computer to the iTunes window under the "Tones" section. The ringtone file should have an .m4r extension.
Once the ringtone is added to iTunes, sync your iPhone by clicking on the "Sync" button in the bottom-right corner of the iTunes window. This will transfer the ringtone to your iPhone.
On your iPhone, go to the "Settings" app and tap on "Sounds & Haptics" or "Sounds" (depending on your iOS version).
Tap on "Ringtone" or "Sound and Vibration Patterns" to access the ringtone settings.
Under the "Ringtones" section, you should see the newly added ringtone. Tap on it to set it as your default ringtone.