Update User Fields from frontend

Hello everybody,

I’d like that my users can update their informations from frontend overriding the previous ones, of course. For example I’ve inserted a “bio” input inside their frontend profiles which should override the core WordPress user bio. This is the code.

$description = trim($_POST['user_description']);
update_user_meta($uid, 'user_description', $description);

and in html code:

<p><textarea rows="5" name="user_description" class="do_input info-description" placeholder="<?php echo __('Insert a brief presentation of yourself.','ProjectTheme'); ?>"><?php echo get_usermeta($uid,'user_description',true); ?></textarea></p>

What am I doing wrong?
Thanks.
Emanuele.