I need to increase my MTU settings on my router for Xbox LIVE.

I don't think it's up yet so I would leave it.

By default, the router can be accessed using Internet Explorer then typing in 192.168.1.1 on the address (hit enter or go).

Leave username blank and type admin as password (default settings).

Under Setup-->Basic Setup

On that page, you will see MTU under Optional Settings. Set MTU to manual and enter the desired size.

You can do that by configuring your router. Look for the default ip address of yoour router, it can be found in your router's manual. After you found it, run internet explorer and type in your ip address (ex. 192.168.10.1). There you o just enter your username and password and your on your way to the configuration process. Go to internet setup and under DHCP Internet Connection Type you can change MTU there. Just give it a try...