How can I disable the password protection?

To disable the password protection you need to do some code changes. Open imgbrowser.php and simply replace
if ($username == "" and $password == "") {
  if(!isset($_SESSION['username'])){
    include(__DIR__ . '/new.php');
    exit;
  }
} else {
  if(!isset($_SESSION['username'])){
    include(__DIR__ . '/loginindex.php');
     exit;
  }
}
with:
$_SESSION["username"] = "disabled_pw";

Check out the Documentation or the Plugin FAQ for more help.