sign_in.html

                <!--  Input user register form 1 -->
                <div id="inputuser" class="col-sm-6 header-content-feature">
                    <div id="register-form">
                        <h3 class="log-title">Accede a tus resultados<br><span class="text-primary">de laboratorio</span></h3>
                        <hr>
                        <h3 class="log-text">Digita tu nombre de usuario</h3>
                        <div class="form-group">
                            <input type="text" class="form-control" id="email" placeholder="...">
                            <div class="help-block with-errors"></div>

                            <a href="#pricing" class="page-scroll"><small>¿Dónde veo mi nombre usuario?</small></a>
                        </div>

                        <!-- log-line -->
                        <div class="log-line reg-form-1 no-margin">
                            <div class="pull-left">
                            </div>
                            <div class="pull-right">

                                <a href="#">
                                  <button type="submit" id="slideRightBtn" class="btn btn-md btn-success-filled btn-log btn-pill"><span>Siguiente</span></button>
                                </a>
                                <div id="msgSubmit" class="h3 text-center hidden"></div>

                                <div class="clearfix"></div>
                            </div>
                        </div><!-- / log-line -->
                    </div>
                </div><!-- / col-sm-6 -->
                <!-- / Input user register form 1 -->

                <!-- Password register form 1 -->
                <div id="inputpassword" class="col-sm-6 header-content-feature">
                    <div id="register-form">
                        <h3 class="log-title">Accede a tus resultados<br><span class="text-primary">de laboratorio</span></h3>
                        <hr>
                        <p class="log-text">Digita tu contraseña</p>
                        <div class="form-group">
                            <input type="text" class="form-control" id="email" placeholder="...">
                            <div class="help-block with-errors"></div>
                            <a href="#"><small>¿Olvidaste tu contraseña?</small></a>
                        </div>

                        <!-- log-line -->
                        <div class="log-line reg-form-1 no-margin">
                            <div class="pull-left">
                            </div>
                            <div class="pull-right">
                                <button type="submit" id="reg-submit" class="btn btn-md btn-success-filled btn-log btn-pill"><span>Acceder</span></button>
                                <div id="msgSubmit" class="h3 text-center hidden"></div>

                                <div class="clearfix"></div>
                            </div>
                        </div><!-- / log-line -->
                    </div>
                </div><!-- / col-sm-6 -->
                <!-- / Password register form 1 -->

signin.js

    $(document).ready(function() {

      // $("button").click(function(){
        $("#inputuser").addClass('animated fadeInRight');
        $("#inputpassword").hide();
      // });

      $("#slideRightBtn").click(function(){
        $("#inputuser").addClass('animated fadeOutRight');
        $("#inputpassword").show();
        $("#inputpassword").addClass('animated fadeInRight');
      });

    });