Welcome to Flyertalk! Am not familiar with CO, but you can upgrade a DL codeshare ticket for travel on AF from the U.S. to CDG only. You must purchase a DL Y/B/M fare. The upgrade does not extend beyond CDG. For example, on an LAX-CDG-MUC trip with all segments operated by AF, if available you may be able to upgrade LAX-CDG but not CDG-MUC.