Follow below steps to change the application pool from IIS

1. Login to your VPS via Remote Desktop. Open IIS Manager (Start > Run > Type inetmgr and hit enter).
2. Under the Connections Pane, expand the VM hostname. Expand Sites and select the website whom application pool you wish to change.
3. After click website name>Under the Actions pane, click on Advanced settings.

4. Select the Application pool option and click the Browse button.

5. Select the Application pool from the drop down menu and click OK. Click OK again to close the window.