How do you get the default ringtone off

Hi DreamFaery,
I understand that your iPhone is not using the ringtone that you originally assigned. Let's see if we can get that sorted out.
I would first look at your settings to ensure that the ringtone is set and not assigned to one specific contact. If it is, make those changes in Settings > Sound > Ringtone and choose the ringtone that you want. The link below will have more details.
Ringtones and vibrations
http://help.apple.com/iphone/9/#/iph37c04838​
If It does not stay, then you may want to reset the settings on your iPhone. This will not erase any content off your iPhone, but it does put all the settings back to their defaults. You can reset the settings at Settings > General > Reset, tap Reset All Settings and follow the prompts. More details are below.
Reset iPhone
http://help.apple.com/iphone/9/#/iph7a2a9399b
Let me know if this helps.
Have a good day.

just go to the settings tab and under sound you can change the ring tone. You can also set different ring tones for different contacts in your phone.