How to customise wp-signup.php on my site

Hi there,

I would like to customize user name/email white fields and "next" button cause their on my site(http://www.myfashion.lt/wp-signup.php) looks really huge and weird.
I was trying to find how to do it on wp-signup.php but looks like there is no these fields customization on it.
Thanks in advance

my test site adress