As we all know the design of IIS 7 had some drastic changes.
One of them is the location where you can bind or change application pools. These settings a simply hard to find some times. To change a specific application pool follow these steps.
1. Open IIS admin console
2. Expand the website folder
3. Click the website you want to change
4. On the right side of your sceen a menu appears
5. Click 'Basic Settings'
6. Select the Application Pool you would like to bind in the pull down menu
7. Click OK
8. Run IISRESET