Congratulations on your new boots.
Depending on how much longer the new boots are compared to your old ones (a few mm should be fine), you can adjust the "length" of the binding by loosening the foward pressure.
That being said, I highly recommend you to take your skis and boots to a shop, since you have no experience in adjusting bindings. It's not to appear judgemental, but the fact that you don't even know where and what the DIN screw is, i wouldn't hesitate handing it over to a professional instead. And please don't start fooling around with your DIN's unless you know what you're doing, you're better off a few dollars poorer but with intact knees, than the other way around.
Should you prove hell-bent on adjusting them yourself, check out this guide:
Best of luck.