How to programatically update existing user profile field in drupal 7
You just need to load the user using drupal function 

profile2_load_by_user($account-&gt;uid, $type_name = NULL)


$account-&gt;uid => user id

$type_name => one of the profile types of profile 2 if any otherwise NULL

   $profile =  profile2_load_by_user($account, $type_name = NULL)
   $profile-&gt;field_headline[$lang][0]['value'] = 'update Software Engg';
   profile2_save($profile);


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Hope it will work for you!