Right-click the network connection icon on your taskbar, then choose Open Network Connections.
Right-click the network connection you want to change.
From the list of options, select Status from the menu.
You can then select Properties.
From the menu, highlight Internet protocol TCP/IP and then click the Properties button.
You will see a couple of options, the first is Obtain IP Address Automatically. But we want to select the second option: Use the following IP Address.
You'll need to enter both an IP address and a Subnet Mask. Since you're behind a router, you should already know your IP address is something like 192.168.1. x (where x is a number). Your router probably already has an IP address like 192.168.1.1, so you will increment the final didgit by one for each PC. So the first computer you change to static IP address will have an IP address of 192.168.1.2 and a subnet mask of 255.255.255.0.
Under the Default Gateway, put the internal IP address of the router, because this is the computer's gateway to the Internet.
Under the Use The Following DNS Server Address. You can get those address from your ISP. Or, this infor might already be viewable inside of yor router's setup.
You will need to make sure thet DHCP is turned off in the router's setup.