How to add ringtones to contacts iphone 4s?

Ok well my mom got a iphone 4S and wants to add ringtones to certain contacts and i downloaded some free ones from some of the apps available from the store but i don't know how to get those downloaded ringtones onto the contacts help?

Added (1). I've done that already the customs i downloaded don't show up

To get them to certain contacts:
1) Go to Contacts
2) Scroll to the contact that you want to assign a particular ringtone for
4) Click on the Contact
5) Scroll down to Ringtone option
6) Select Ringtone Option and choose which Ringtone you'd like to assign to that particular contact
7) Click on Done in the upper right hand corner to save these changes

If you mean you can't find them, then plug in the phone and go on itunes.go to your iphones name and then at the top click apps. Then scroll down to find whatever ringtone app you used and download them to your pc.find the downloaded files and drag them to itunes and to the phone.

another recommendation for ringtone apps that i liked is ringtones #1. Where you find a ringtone, create a ringtone, or record your own in one app. When you are done, just send the ringtone file from your phone to your email address.download the file from your email account and drag the file to itunes and to your phone