Steps:

1. Launch the “Server Manager”

2. Click Role, Click “Add Roles” in the right panel

3. Click Next, Select the checkbox of “File Services”, Click Next.

4. When the “Select Role Services” appears, select the checkbox of “Service for Network File System”

5. Click Next, Click install.

Source: http://social.technet.microsoft.com/Forums/en-US/winserverfiles/thread/8ac66914-1e23-40ad-bbfa-bb36c32cedf5/

Important Note: Sorry for the wrong information at first, as the Microsoft document is actually missing!