How should I be keeping track of a php script's versions/changes when it pertains to a single script in one file?

Should I have a separate changelog, and if so (1) what should it be named, (2) how should the contents of the log be formatted, and (3) how should the log be associated with the php script/file?

Or, should I include the changes in a comment at the top of the php file? Currently, I have the following comments at the top of the file:

```
/**
 * @author    John Doe <contact@John Doe.com>
 * @version   1.0
 * @copyright Copyright (c) 2010, John Doe
 */

```

Thanks in advance for your response!