How to Increase Memory Allocated to IIS .NET Application?

The CLR hosted in the application pool for the web application will grab as much memory as necessary and then based on memory demand, use garbage collection as needed to free up memory.

You can put limits on the amount of memory accessible to an application pool (in the UI, via the Advanced Settings dialog, or via PowerShell and the WebAdministration module).

You might want to check if there are caps already set for the memory on the application pool, but there really isn't a way to dedicate more memory directly to an app pool without editing the machine.config for the .NET version the app runs under.

EDIT: The default autoconfiguration for memory caps in IIS 7 is 60 percent of the machines RAM. This can be manually increased by editing the machine.config file for the .NET version that your application runs under. Details of the various configuration settings here.