The iPhone has a limited choice of ringtones but the default ringtone can be changed. For this purpose, your desired music must be cut to 30 seconds and the format has to be changed to ACC. This version must be changed again to M4r format to sync to the iPhone and it will appear accordingly in the iTunes's ringtone folder. The PC and the Apple phone must be synchronized so there will be no shortage of ringtones. With the inventions in telephony, the phone will be always ready to play a new ringtone.
I want to change the default ringtone on my iPhone
Firstly, to cut music to make your ringtones go to iTunes:
Right click on your music
Click "Get Info" and a window will open
Go to the Options tab and you can set the "start" and "end" point of the track
Change it to 30 seconds then click OK.
Change the music format to ACC:
Right click on your music cut to 30 seconds and you click on Create ACC Version.
After the music is in ACC (the conversion is fast), you will find it in your iTunes folder
Change the extension to .m4r to change it to ringtone format
It should now appear in your ringtones folder of iTunes
You need only synchronize your iPhone and PC to have your new ringtones