And to add to Dell's info....
Depending on how you created your WEB app depends on the setting for the CPU and project...
If it's a WEB app then it's all up to IIS as to when platform it runs in and which SDK to deploy on the IIS server.
So if you ahve no option in VS to set the platform, x86 or x64 then you can simply deploy the 64 bit MSI on the WEB server and the app should run. You'll need to make the framework and permissions are configured for your app.
In IIS change the platform this way for your App Pool:
Don