Select the item to be deleted in the Resource Tree view. Press the Delete button on the tool bar or use the hotkey combination [Shift-Ctrl-D]. Items selected for deletion are indicated by an x marker.

To restore deleted items, use the Undelete button on the toolbar or use the hotkey combination [Shift-Ctrl-Z].
Changes are made permanent only after you have saved them to the file.

Select 'File' -> 'Save File As ...' to save the changes you've just made to the target file. If warned that the image size has changed, click "Yes" to update the file size.