I'm flying international to santiago but with a stopover in houston.

In my 'upgrade' options for the flight it offers upgrade for miles but also says i can use an RPU. The houston leg is waitlisted but there are seats available on trip to santiago

It doesn't make any mention that the upgrade would apply only to a portion of the trip. If I select RPU will that upgrade me for the whole trip or would it only bump my status for upgrade to houston?


Additionally, I don't care if i'm upgraded to houston. Can i get a cheaper upgrade by only upgrading the international portion? If so, how?