If you have ordered additional IP address(s), you will be send an email that contains your new IP address (or IP range if more than one address) as well as the Subnet Mask.
To add the IP(s) to your server:
Go to your START MENU, and in the search box, type view network connections, and select this option from the search results:

Right-click on your Local Area Connection, and select Properties:

In the Properties window, select Internet Protocol Version 4 (TCP/IPv4), and click Properties:

In the TCP/IP Properties window, select Advanced:

In the Advanced TCP/IP Settings window, in the IP Addresses section, click Add

Now enter the IP address and Subnet mask that you were provided with:
(THE DETAILS BELOW ARE JUST AN EXAMPLE, BE SURE TO USE WHAT WE SENT YOU)

Click Add and click OK (on all three windows to save and exit)
The new IP address will now be available to your server.