I agree with RJ's answer - if you need to do it programmatically, Powershell is the easier option. However, if you just need to update the email address on the one user, you could also do it manually in the user's profile via Central Administration (assuming you have access).
Something to keep in mind is that by default the email address is pulled down from Active Directory (or whatever your authentication provider is) when the profile sync runs. If the address is wrong in AD, it will need to be updated there first - otherwise you can update it manually in the SharePoint profile, but it will most likely be overwritten by the incorrect one from AD again.
If it's wrong in both places, just correct it in AD and run a full profile sync. An incremental should catch the change, but in my experience it doesn't always happen.
Note: I'm assuming here that you're a SharePoint Admin trying to update a user's email address. If the code is part of an application or a custom form, then obviously that's a different story altogether.