You can use the Remote Agent Utility to remove an Oracle instance for the Oracle Agent on Windows computers.
To delete an Oracle instance on Windows computers
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On the computer on which the Remote Agent is installed, on the taskbar, click Start > All Programs > Symantec Backup Exec > Backup Exec 2010 Remote Agent Utility. When the Remote Agent Utility is running, an icon appears in the system tray. You can double-click this icon to view the utility. 
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On the Oracle tab, click Delete. Any instances that currently exist on the computer appear on the tab.