How to display user form and hide some fields? I'm building a website which has a member section. People subscribe and complete the "user" form (username, email, password and some other fields).

For an additional fee, they can be part of the "dating" part of the website, where they can meet new people.

After paying, I would like them to complete a form about them (height, eyes, etc.). Those fields are already in the user form.

I'm displaying the user form this way : 

global $user;
module_load_include('inc', 'user', 'user.pages');
return drupal_render(drupal_get_form('user_profile_form', $user));


How would i go about hiding some fields that I don't want them to see/modify?

Thanks!
You should alter the form before rendering it.

$form = drupal_get_form('user_profile_form', $user);

// Uncomment this line to inspect the structure of the form array (needs devel module)
//dpm($form '$form');

// hide field.
unset($form['field_name']);

return drupal_render($form);