You can use the Style Manager to delete custom node styles from Task Assistant Manager.
- Start ArcMap.
- If necessary, click the Task Assistant button on the Task Manager toolbar to display the Task Assistant window.
- Right-click in the Task Assistant window and click Style Manager.
The Style Manager dialog box appears.
- Click the Styles drop-down arrow and choose the style you want to delete.
- Click Delete.
- Click Yes to confirm that you want to delete the style.
- Click Close.