Update joomla password

$plaintext=$_POST['password'];
function getCryptedPassword($plaintext, $salt = '', $encryption = 'md5-hex', $show_encrypt = false)
{

// Get the salt to use.
$salt = JUserHelper::getSalt($encryption, $salt, $plaintext);
$encrypted = ($salt) ? md5($plaintext.$salt) : md5($plaintext);
return ($show_encrypt) ? '{MD5}'.$encrypted : $encrypted;      
} // END getCryptedPassword
$password = getCryptedPassword($_POST['password'], $salt= '', $encryption= 'md5-hex', $show_encrypt=false);
echo $password;