Dendence

Good evening, i am new at this stuff and have a question.I got a good deal on a 4 ch H264 dvr from ebay. I am really happy with it . I have enabled port forwarding and can remotely access the dvr through internet explorer. The one problem that I have is that i can't change the user name and password from admin, admin in any of the dvr settings. So anyone with my IP address has full control of my dvr.Any help would be appreciated. Thanks

I paid $100. Can I put the link up on here so you can see what it is ?