There are many ways to change the format of the audio file. You can use special editing programs, you can use converters, But each in turn.
One of the most popular options is the editing program "Sony SoundForge". Here everything is simple: install the software (if not installed), run. A window opens. If the program occupies the entire screen, you can collapse it to the desired size (that's everyone decides for himself).

So we see a gray background. And on the desktop is this playable audio file. Click the mouse shortcut ringtones, and drag it to the gray background open program. Immediately is processed, and is displayed in the track edit audio, where music is presented in the form of vibrations. Allocated to the whole period of these oscillations, we find in the top menu "file", look for "Save as..". Activate. A new window appears where we are prompted to choose a save location a new file, its name and format. That's just there and you can choose what we need. Put, say, mp3 format. Click "save". The operation was successful. The file is saved in a new capacity.
You can use converting software such as "Hamster Free Video Converter". The process is similar to that described above. Difficulties in working with this program will not occur.
There is another option, no less effective than the above two. Click the right button of the mouse on the audio file is unreadable, thereby causing the context menu. Look for "rename". Assigned any name. And give it the extension that we need. This is done simply. After file name put a dot and then enter the desired extension (for example, mp3). In the end the file will look like this: "music.mp3. The conversion will happen automatically. Again the file was readable.