How to delete SQL Server Instance ?

To begin the uninstall process, from the Start menu, click Control Panel, and then double-click Add or Remove Programs.

Select the SQL Server component to uninstall, and then click Change/Remove. This starts the SQL Server Installation Wizard.

Setup Support Rules runs to verify your computer configuration. To continue, click OK.

On the Select Instance page, use the drop-down box to specify an instance of SQL Server to remove, or specify the option to remove only the SQL Server shared features and management tools. To continue, click Next.

On the Select Features page, specify the features to remove from the specified instance of SQL Server. 

Removal rules runs to verify that the operation can complete successfully. If Setup detects SQL Server 2008 on this machine, you will see a warning. Uninstalling shared components could render the SQL Server 2008 instance unusable. For more information see Considerations for Side-by-Side Instances of SQL Server 2008 R2 and SQL Server 2008.

On the Ready to Uninstall page, review the list of components and features that will be uninstalled.

The Setup Progress page displays Setup status.

On the Completing Setup page, click Close to exit the Installation Wizard.

Repeat steps 2-9 until all SQL Server 2008 R2 components have been removed.