Allow user to choose/change role/level

Hi there just had a question about user roles.

I want to allow users to choose from different roles. I am using Role Manager to create the roles.

Is it possible to create a drop down menu in the registration that would allow users to pick a role…? Or would it make more sense to allow the user to change their role after registration with something like below?

<?php get_userdata($userid);
      $userlev = $user_info->user_level;
      echo $userlev; //displays user current level

update_usermeta($userid,'user_level',$newlevel); //use this to change user level/role???
?>

Is there a tag/codex to change the user role, as this would only change the level?

Thanks guys for any help!

TC