Change names for "Username" and "Password" fields on sign up page

We need to change names of "Username" and "Password" fields on sign up page http://qa.jtalks.org/jcommune/user/new to make them look corresponding to the ones on sign up pop-up window.
The specification about the fields' length is not important, as it is duplicating the information user can see in the error message, once he enters data with wrong length to the field.

Acceptance criteria: