"This upgrade may be used on a standby basis, subject to availability, on the day of travel on any eligible Lufthansa flight in accordance with the terms and conditions of this certificate, except when booked in LH booking classes X, I, R, N, W, S and E. In addition L and T fares are also excluded for Intra-Europe flights."

Also, "Some Internet sites, such as Priceline.com and Hotwire.com, issue tickets that are not upgradeable. Please check with your Internet site for terms and conditions."

So as long as you are not ticketed in XIRNWSE then you should still give it a try at check-in.