Issues converting ASPX Web app from .net 3.5 to 4.8.1

I have an older ASPX Web application that I need to upgrade from .net 3.5 to 4.8.1 because we need to move to Windows Server 2022. I am having a hard time finding good resources online around this. Can someone point me at any good articles or give me some steps here?

Ok, so we assume that the .net 3.5 site builds from Visual Studio, correct?

so, why not change the .net framework to 4.0, and see if the project builds.

So, this:

If the project builds?

Then change to 4.8.1

If the project also then builds, then you are quite much done.

So, the first goal is to ensure that the project builds fine as .net 3.5.

If that works, then try 4.0, and build again.

And as noted, if 4.0 works, then try building with 4.8.1

If the project builds, then you just upgraded and are now running 4.8.1.

I find in many cases, that 3.5 applications often upgrade very easy, and a good number of them only required changing the framework and a building the application.

It not clear why many are suggesting that a lot of effort is required for such upgrades, and in the past I have found that a simple upgrading of the project framework from 3.5 to 4.0 and building works fine.

As noted, if the project builds with .net 4.0, then try 4.8.1.

If the project builds, then you just upgraded to .net 4.8.1, and no further code changes are required.

If the projects builds, then try running and testing it. If the project builds and runs? Then this simple change of the .net framework is all you require.