Go to contacts
First of all on your home screen find the contacts icon. It has an icon of a red box with a hollow white person in it. The logo may vary depending on the version of your Android. Tap the icon once and the contact list will open.
Scroll down to locate the contact
Either scroll down or search for the contact by name for which you want to set a ringtone.
Edit the contact
Long press the contact button. A sub menu will appear, tap the edit button once. The contact information will appear on the screen. Scroll down and tap the option Ringtone once.
Select the ringtone
A sub menu will pop up. It will have three options, Default ringtone, and Select sound from my files, Phone ringtone. Tap the second option and the device will open the memory card and ask for you to locate the ringtone.
Browse through the folders to find the ringtone. Tap the sound file once and it will be set as the ringtone for that contact. Press ok to save the contact and exit the contacts.