Can't Open Machine!

This is one of my inherited machines, but I have no idea how to open it! Do I have to find a square tool? Or is that screw for something else? I've had it now for 5+ years and I would love to see what's under this case! It's so heavy and I just know I'm going to be in love, but I'm so scared of breaking it! Am I overthinking this? Is it something simple?