title: Cannot upgrade to .NET Core 3.0 from 2.2, or .NET Standard 2.1 from 2.0, using VS2019 16.3.x
body: <p><em>What I want to do</em>: Upgrade to the latest core and standard versions for my apps and libs that the apps depend on. These apps and libs are currently on 2.2 (latest) and .Net Standard 2.0 for libs.</p>
  
  <p><em>What have I tried</em>: I have installed the latest versions of all the SDKs, runtimes and the latest IDE of 16.3.2 - I want to attempt to target .NET Core 3.0 and .NET Standard 2.1 for my libraries. </p>
  
  <p><strong>I cannot do any of these things either directly, or by manually messing with project files.</strong> It is <em>not</em> in the dropdown for existing projects and if I manually edit the project file, I get an error saying that 3.0 is not a valid SDK version.</p>
  
  <p>If I spawn a new IDE and create a new web app, console app or class lib, I can easily target 3.0, or NetStandard 2.1 - which is fine and proves that it's all installed... but what I don't understand is how to plot a path to migration/upgrade - creating brand new solutions and projects and attempting to recreate the software isn't really an option.</p>
  
  <p>Am I missing something here? The Internet is only really useful for guiding people to how to turn on .NET Core 3 back when it was a preview version, which obviously is no longer the case.</p>
  
  <p>There must be a set of steps to help people migrate from 2.2 core or 2.0 standard ...</p>