I am planning to fly IAH-FRA on UA, and continuing on FRA-GVA on LH. There is upgrade space available on the IAH-FRA flight in the RN inventory. There is also upgrade space available on the LH flight in *their own* I class inventory.

Can I use my Mileage Pluss miles to upgrade both the UA *and* the LH flights? Or do I have to purchase a separate upgrade for the LH flight from LH using their own frequent flyier program?

(In case you are wondering, the return will be GVA-EWR-IAH, all on UA, with RN availability on both segments.)

Thank you!