Hi there
If you upgrade your fare you get 40kgs allowance on JK (which is very generous, most airlines give either 30kgs or 2 pieces allowance at "real" Business Class fares).
If you want to be certain not to have any problems, take 2 pieces and make sure that neither is more than 23kgs and that they together are not more than 40kgs (depending on the airport/handling company and the individual check-in agent, they might have a little additional tolerance of a few kgs, but better do not count on this).
Have a nice trip and enjoy Barcelona!