You can use these docs for uninstalling your 2005 sql instance based on your requirement.

Uninstalling an instance of SQL Server 2005 manually

Windows Installer Clean-Up Tool

Uninstall SQL Server Management Studio;EN-US;909953

Using the Add or Remove Programs item in Control Panel to add
or remove components for stand-alone installations and clustered
installations of SQL Server 2005 (KB: 922670);EN-US;922670

Uninstall SQL Server Express

Fatal error during installation

Uninstall Applications NOT in Install/Remove Programs List