add ringtones to iPhone 5c

Hi,

I've been trying to add a ringtone to the iPhone 5s. However it is getting me increasingly frustrated with the device. Especially since tethering is a pain as well... Anyway... I've followed the doc:

How to sync ringtones to your iPhone

However I can't seem to find the sync settings and the tones remain grayed out after dropping them on the tones tab. I have confirmed that it says ringtone in the info so that it is indeed a ringtone.

Anyone the golden tip? I'm using a macbook pro, with the latest 12.3.3 iTunes.

Kind regards