I've done this.
But I used KVS Tools to tell me whether or not there's an upgrade available first. When it showed me CS1, I called Marco Polo to see if there was indeed an upgrade available. Sometimes what appears in KVS might no be an upgrade redemption but it could be a full redemption or companion.
Once MP confirmed it was an upgrade redemption, she helped me to change my fare from E to W and then proceeded to issue me the upgrade.