Open the iTunes Store app on your iPhone
Tap More
Tap Tones
Browse free tones if available
Tap the tone you want
Tap Get or Download
Use GarageBand to create a custom ringtone from a song or sound file
Save the GarageBand project as a ringtone
Set the ringtone in Settings
Go to Settings
Tap Sounds & Haptics
Tap Ringtone
Select your downloaded or created ringtone
Download free ringtone files from trusted websites on a computer
Transfer the ringtone to your iPhone using GarageBand or Finder
Avoid unofficial apps that ask for suspicious permissions
Check that the ringtone file is in M4R format
Make sure the ringtone is under 30 seconds long