Alter drupal registration form

Dear experts,

I am trying to alter drupal registration form. But I am quite confused how to do it.

The first thing I am trying to do is to add some intro text to the form. To do that I added the following to my template.php file:

function adaptivetheme_subtheme_theme() {
  $items = array();
  $items['user_register_form'] = array(
    'render element' => 'form',
    'path' => drupal_get_path('theme', 'adaptivetheme_subtheme') . '/templates',
    'template' => 'user-register-form',
    'preprocess functions' => array(
    'adaptivetheme_subtheme_preprocess_user_register_form'
    ),
  );
return $items;
}

function adaptivetheme_subtheme_preprocess_user_register_form(&$vars) {
  $vars['intro_text'] = t('Join us!.');
}

Then I created a user-register.form-tpl.php to render the form like this:

<p><?php print render($intro_text); ?></p>
<div class="yourtheme-user-login-form-wrapper">
  <?php print drupal_render_children($form) ?>
</div>

Now what I want to do is to change the labels to the form in order to show differently on the user profile page. for example. In the register form I ask: Tell us about yourself (text field).  On the profile page I would like that to change that label to About Me.

Could you please please please guide me to do this? I am not sure if I should create a custom module and add the corresponding hooks… not pretty sure, I´ve been just reading couple of things that are making me even more confused.

I would greatly appreciate any help,

Winter