1) Stop all SQL Services.
2) Uninstall all Microsoft SQL services in Control Panel
3) Delete all files in %Program Files%\Microsoft SQL Server directory
4) Open REGEDIT32 and delete key “HKCU\Software\Microsoft\Microsoft SQL Server”
5) Open REGEDIT32 and delete key “HKLM\Software\Microsoft\Microsoft SQL Server”
2) Uninstall all Microsoft SQL services in Control Panel
3) Delete all files in %Program Files%\Microsoft SQL Server directory
4) Open REGEDIT32 and delete key “HKCU\Software\Microsoft\Microsoft SQL Server”
5) Open REGEDIT32 and delete key “HKLM\Software\Microsoft\Microsoft SQL Server”
Use REGEDIT32 on your own risk.