...
id (Required). Number. The ID of the user to be updates
name(Optional) String. Either the first, last name or both must be present.
login (Optional). String. Login name of the user. If login is present, the user will be counted towards your license count.
password (Optional). String. Password of the user.
email (Optional). String. Email of the user. For users with login, email is mandatory.
All other fields are same as those for the create users function.
When your data format is XML, you should post something like this:
...