You will need to open the set up page of the router.
Once you open the set up page of the router, you will find application and gaming tab at the top. click on it. Just below the application and gaming tab you will find PORT FORWARDING sub tab. click on it.
On this page you can open the ports. If you are not able to change any setting on this page OR if it is grayed out, then you will need to upgrade the firmware of the router. This router has issues with the firmware.
download the correct firmware and upgrade the firmware.
Click here for step by step instructions