I need a website where I can change my DNS

So I registered with a new host for my company. All set up and stuff, but the problem is I need to change the DNS of our domain name, dp3marketing.com, to the new server. The larger problem is that my boss doesn’t remember where he got the domain name, nor any user/pw information for a domain-site so I can go in and edit the DNS…

So my question is does anyone know where I can go to say “Hey, I own this domain name. Let me change the DNS through you” kind of thing?

Help me guys! Please :).