How do I setup the WPS PIN on my Wireless N 300Mbps Router?

Please refer to the 'configuring via web browser' section of the user manual at the link below:

There is a step-by-step setup wizard that you will be required to follow prior to setting your PIN.

When you get to the Wi-Fi Protected Setup (WPS) section, select the PIN option and you can then set the PIN for the device.