Correct way to uninstall SQL Server 2008 ( or above )
That's pretty much all there is to it. You may want to backup or transfer your database files/backups before the un-installation process, but getting rid of the application is that simple.

As per Mirosoft Support KB 955499,


  
  Open the Programs and Features item in Control Panel.To do this, click Start, type appwiz.cplin the Start Search box, and then click
  appwiz.cpl in the Programs list. 
  Select the SQL Server component to
  uninstall, and then click Change/Remove. This will start the SQL
  Server Installation Wizard. 
  Setup Support
  Rules will run 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. To
  continue, click Next. 
  Removal Rules will run to verify that the
  operation can complete successfully.  
  On the Ready to Uninstall page,
  review the list of components and features that will be uninstalled.
  The Setup Progress page will display Setup status.
  On the Completing Setup page, click Close to exit the Installation Wizard. 
  Repeat
  steps 2-9 until all SQL Server 2008 components have been removed.