You're probably not going to get a definitive answer as this isn't a television techy forum but I'll try my best..
I assume ivacy vpn is similar to hide my ass in that it is sftware you download and when switched on tricks the internet into thinking you're in another country. I'll go on to assume you're wanting to change theIP of your apple tv to access content from another country (maybe netflix?)? The issue you will have is that these programs change the IP address solely for the devce they are being used on and NOT for the router you're using. So.... unless you can get the apple tv connect to the internet through your computer with the software running, ivacy vpn is of little or no use.
Easiest way to watch netflix (or similar) from another country would be to turn on your vpn, log in to your netflix (or similar) account online on your computer and then stream the content to the apple tv box using airplay.
Alternatively, you could go down the route of trying to find out how you change the IP of your router.
You need a router with point to point tunneling (pptp) vpn features to get this working properly with the appletv because the appletv doesn't have the required options to change this type of thing. There is a guide on the Ivacy site how to do this.