Edit the header template:

Admin CP -> Styles & Templates -> Style Manager -> Edit Templates -> header

And change this:

Code:
<div id="remember" class="remember">
                    <label for="cb_cookieuser_navbar"><input type="checkbox" name="cookieuser" value="1" id="cb_cookieuser_navbar" class="cb_cookieuser_navbar" accesskey="c" tabindex="103" /> {vb:rawphrase remember_me}</label>
                </div>
To this:

Code:
<div id="remember" class="remember">
                                       <label for="cb_cookieuser_navbar"><input type="checkbox" name="cookieuser" value="1" id="cb_cookieuser_navbar" class="cb_cookieuser_navbar" accesskey="c" tabindex="103" checked="checked"/> {vb:rawphrase remember_me}</label>
                                </div>