The answer varies depending on which type of finger information you want to change. When someone on Athena simply types "finger username", they get some basic information about you. For example:
This information can be changed by running the "chfn" program. It will prompt you to update the various pieces of information (or press "Enter" to accept the current setting). Once updated, the information will take a few hours to take effect, and may take longer to propagate to the machine you're currently using.
The "finger username@mit" or "finger username@mitdir" commands, however, display slightly different information:
This information comes from the MIT directory. Students can update their MIT Directory entries using WebSIS. Faculty and staff can update their MIT Directory information using Atlas. The information may take several days to be updated in the directory, and can take up to 2 weeks at the beginning of a semester. Students who have questions about their Directory information should contact the Registrar, and faculty/staff should contact Human Resources.