Clickonce .net upgrade

If the user has .NET 4 installed and your application targets .NET 4.5, they have to install .NET 4.5.

.NET 4 will not automatically be updated to .NET 4.5. At some point, Microsoft will start pushing out .NET 4.5 in Windows Updates, but it's way too early to anticipate the timing on that.

If the user has only .NET 4 installed, they would need to install .NET 4.5 prior to installation.

Your ClickOnce application should have .NET as a prerequisite and prior to installing app, you can install .NET.

How to: Install Prerequisites with a ClickOnce Application

How to: Specify a Support URL for Individual Prerequisites in a ClickOnce Deployment