Make sure the file is mp3 format, 600 kb or smaller, and 30 seconds or less. You can make your own ringtones at the following sites:
Once you have your ringtones ready, there are many different steps you can follow depending on what you have available on your phone.
1. If you have internet/text messaging: sites like cellsea and myxertone will provide you with instructions.
2. If you have a usb cable: connect your phone making sure it's in Mass Storage Mode. You can do this by going to settings, connection, usb connection mode, mass storage. Open the folder for your phone on your computer. It should be one of the choices of storage when you go to My Computer. Place your ringtones into the Sounds folder. And voila! It should be in the ringtone menu in your phone.
3. If you have a MicroSD memory card: Create a folder on the memory card. Name it anything other than Music (the phone will automatically create a Music folder which can not be used as ringtones). Once you insert your card into your phone, the tunes should come up when you open your ringtone menu!
Hope this helps! Good luck! :)