Load and submit user profile form
If oyu want to get and submit a form programatically you must use the function drupal_form_submit


  Retrieves, populates, and processes a form.
  
  This function allows you to supply values for form elements and submit
  a form for processing. Compare to drupal_get_form(), which also builds
  and processes a form, but does not allow you to supply values.


Check this function's documentation page and its comments for some examples.