If you have inserted a drawing (DWG) as an xref, you can use this method to convert attachments to overlays or overlays to attachments. 
Note: You cannot change the type for nested xrefs. 
 -  Click   Find . Find .
- In the External References palette, File References panel, change the type using one of these methods: - To change a single reference: In the Type column, double-click the cell to toggle between Overlay and Attach.