First, in Windows, click Start, Administrative tools, and Internet Information Services (IIS) Manager.  Then select your server name (the second item in the left column under Start Page).

At this point you should probably create a new application pool separate from the default application pool.  Right click on Application Pools, and select Add Application Pool . . .

Insert a friendly name for this new Application Pool.  Select the version of ASP.net framework that may be required to run the site / application, or select No Managed Code if no .Net framework is required (such as if your website functions on serving PHP pages. Leave Managed pipeline mode as Integrated, check the checkbox to Start Application Pool Immediately, and click OK button.

Right click on the name of the new Application Pool that you just created, and select Advanced Settings.

Click on “ApplicationPoolIdentity” (which is the value across from the Identity field shown below) and then select Network Service from the pop-up box / list that appears.  Click OK twice to confirm this change.

You can apply the new Application Pool to a new or existing website, or to an new “Application” that you create by converting a major sub-directory path of a Website.  To establish an Application and apply the new Application Pool to that new Application, just right click a sub-directory of a website and select “Convert to Application” from the drop-down menu.

Click the select button to change from the DefaultAppPool and select the new AppPool you just created.  Note that the physical path to this sub-directory is already set.  Then, click both OK buttons to apply and exit these property boxes.

Let me know via comment if this works for you, and if you have anything that I should add to or change in this Article. Thank you.