Your Nokia 216 has a microSD memory card reader. If your personal computer can also read that card type (Most laptops are so-equipped), you should be able to save a music file
The Nokia 216 is equipped with Bluetooth version 3.0 + HS, which lets you connect to your computer wirelessly. Just pair phone and computer together and drag and drop your music files from your computer to your Nokia 216.
Since your Nokia 216 is equipped with a sound recorder (also known as 'voice memo'), a very simple technique involves just putting your phone nearby your computer's speakers, playing whatever song, music or sound you would like as a ringtone, and recording it -- you can even use your voice, your child's voice or even your cat's 'meow!' Record it with your mobile and there you go! Unless that function was specifically blocked on the Nokia 216, you should be able to navigate to the ringtones section and choose your new recording as a ringtone. Of course, the quality will not be optimal but, after all, it's free!
If all of the above tips do not work with your Nokia 216 or if you prefer not to buy new accessories, you can still use one of the numerous free '3G Uploader' services available online. A search on Katapulco should retrieve plenty of them. 3G uploaders are simple: Save your own music on their web site and they will provide a temporary URL. Navigating to that URL with your Nokia 216's browser should download the free ringtone.
More on free ringtones
Here are some of the 100% free ringtones (Nokia 216-compatible) offered here at MartinsRingtones.com:
Free 'Unclassified' Ringtones Free Ghost Ringtones Free Ringtones-a-gogo Free Techno Ringtones Listen To All Our Free Polyphonic Ringtones