Manually Uninstall .NET Core SDK 2.2.0-Preview and 15.5.0-Preview Nightly Builds

# Manually Uninstall .NET Core SDK 2.2.0-Preview and 15.5.0-Preview Nightly Builds

[A change in the version number strategy for .NET Core SDK](https://github.com/dotnet/designs/pull/29) resulted in some nightly builds having a higher version number. This higher version number will block the installation of the correct .NET Core SDK.

If you have installed nightly builds of the .NET Core SDK that start with version number that begin with `2.2.0-preview1` or `15.5.0-preview`, you must manually uninstall these preview builds before later versions of the SDK with version numbers like 2.1.xxx will be available. This may have occurred by installing nightly builds of the .NET Core SDK or concurrent nightly builds of Visual Studio previews.

## Discussion

Please share your thoughts on this change and see what others are saying at:

[dotnet/cli #8652](https://github.com/dotnet/cli/issues/8652)

## Details

[We changed the version number strategy for .NET Core SDK](https://github.com/dotnet/designs/pull/29) as development was ongoing. Because of this, version numbers on the old scheme appeared in nightly builds. Unfortunately, these numbers are higher than the version numbers in the new scheme. All of the newer SDKs for .NET Core 2.1 will be ignored due to this higher version number; this includes newer nightly builds, public previews and eventual releases.

These older version numbers are similar to the following, with the last several different values in the last six digits:

```
2.2.0-preview1-008000
15.5.0-preview-007082
```

Since the newer versions are in the form:

```
2.1.300-preview1-008000
```

## Call to Action

If you have installed nightly builds, please uninstall any .NET SDK versions that start with `2.2.0-preview1` or `15.5.0-preview`.