LONDON, England - McLaren driver Jenson Button is keeping an open mind about how big a step his team will make with an eagerly awaited upgrade package for the Spanish Formula 1 GP.Button, now 33, 2009 F1 World champion and winner of the final 2012 race in Brazil, has finished no higher than fifth in the four so far in 2013 in a car off the leaders' paces.McLaren team boss Martin Whitmarsh said in April that the Spanish GP updates had to deliver a real performance improvement in Barcelona if the team were to stay in the championship reckoning.'LOT OF TALK'Button said on Friday (May 3): "It's been difficult for the team to make consistent progress in the first four races but I think returning to a circuit where we undertook two of the pre-season tests will give us a useful progress benchmark."There's been a lot of talk about the importance of next weekend's upgrades but, as with every upgrade, they're simply part of the continuous improvement made through the season."There'll be elements that work, elements that perhaps work in a way different to what we'd anticipated, elements that don't work or perhaps require further work... I'm pragmatic about what we'll discover (in Spain)."Rivals also expect that to be the case."We know McLaren is going to bounce back. The team has huge resources, it won't lie down," Force India's Paul di Resta said in Bahrain after finishing fourth to put his team ahead of McLaren in the Constructors' standings.McLaren is sixth with 23 points, Force India has 26. Red Bull leads the standings with 109.