<p>Sign Up</p>
<%= form_for @user, :as => :user, :url => new_user_path, :method => :put do |f| %>
  ...
<% end %>

Calendar::Application.routes.draw do
  root "welcome#index"

  get "user/change_pw"
  get "user/forgot_pw"
  get "user/new" => "user#new"
  get "user/sent_pw"
  get "user/sign_in" => "user#sign_in"
  get "user/signed_out" => "user#signed_out"
  get "welcome/index"

  post "user/sign_in" => "user#login"
  post "user/new" => "user#register"
end

<%= form_for @user, :as => :user, :url => new_user_path do |f| %>