if (creatednewalls == 1)
{
    creatednewalls = 0;
    with (topwall)
        instance_destroy();
    with (bottomwall)
        instance_destroy();
}
if ((difficulty == 4 && createdguns == 1) || (difficulty == 6 && createdguns == 1))
{
    with (gun1)
        instance_destroy();
    with (gun2)
        instance_destroy();
}