I've done a bit of Googling and found your router works in the same way as mine.
Before clicking this link, I need you to take note of a few points. His link to your router is broken BUT following the instructions on the page for the BT Voyager 205 will be the exact steps you need to follow.
If you're unsure after reading the pages then get back to me and I'll explain more. He doesn't
explain how to open ports 8000 and 8001 you will have to use your common sense by reading the rest of the site first. Good luck