Delete
Click the Home | Selection | Delete command or press the DELETE key on the keyboard to remove a selected object from the document. An object can sometimes be restored by clicking the Home | Undo | Undo command.
If the object is part of a higher level object and is currently in use by the object, then it cannot be deleted. For example, if a line/scatter plot is using Y Axis 1and you select Y Axis 1 and attempt to delete it, the Home | Selection | Delete command is disabled and the deletion is not allowed. If the line/scatter plot were using a different axis, then you would be allowed to delete Y Axis 1.
To delete a grouped item, select the sub-object in the Object Manager and press the DELETE key