You probably need to show hidden files
first. How to show hidden files in Windows 7
In Windows 7, you will need to run Notepad as administrator. To do so, you will need to find the notepad shortcut in the Accessories
folder and right click on it, then select Run as administrator.
Once Notepad launches, select File, then Open. Navigate to the hosts file path (typically at c:\windows\system32\drivers\etc), then select the hosts file. Make your changes, then save your changes. After you save your changes, you may close Notepad. Changes you make take effect immediately.