Re: transfer ringtones from itunes to samsung s4
Welcome to Android Central! I assume the ringtones are in AAC format, right? Although the S4 is supposed to be compatible with AAC files, I'm not sure if they can be used for ringtones--I think it has to be mp3, wav or ogg. You could always try the AAC file by copying it via USB to the Ringtones folder, then go to
Settings>Sound>Ringtone, and see if it shows up. If it doesn't, you'll have to convert it to mp3.
A somewhat easy way to convert would be to upload the ringtone to your Google Music Library using Google Music Manager. Uploading AAC files to Google Music automatically converts them to mp3. You can then download that file back to your computer from the Google Music Library website, and now it will be an mp3 file. Copy that file to the phone's Ringtones folder via USB, and now try to select it as a ringtone.
Here's an AC article describing the process in more detail:
Android 101: Adding your own custom sounds to Android events | Android Central