How to change #weight of fields added to user register page by form_alter()? I have created some fields on my user registration page named like - 
First Name (machine name - field_first_name),
Last name (machine name - field_last_name) etc..

I want to change their #weight according to me to appear at the place where I like them to be from the form_alter function at my custom module..

For the default name &amp; email I used -

$form['account']['name']['#weight'] = 7;
$form['account']['field_first_name']['#weight'] = 8;


&amp; it worked..

But If I am using for added fields in this way like -

$form['account']['field_first_name']['#weight'] = 6;


It's not working...

Can I get any help in this ?
Account as a whole is in a group which contains the name password etc. The one we add might be out side of that. That is why it is not effecting the weight.