why did they change the director ?

How about using google or find out the sources. The films themselves were not supposed to be movies but a tv series called Millenium. 6 90 minutes episodes, 2 episodes covering each book. The first 2 episodes were Men who hate women ( or what the English call The girl with the dragon tattoo) and they got a better director and bigger budget for that because they also planned to release a shortened version of that into movie theaters. They did and it became a huge hit. Because the success of that movie they decided to the same with the other 4 episodes. Take episode 3 and 4 and turn it into a movie by cutting 50 minutes out of it and Episode 5 and 6 and also cut some scenes out and make a movie. Movie number 2 and 3 had a lot less budget that movie no.1 because they never meant for it to be shown at a cinema but directly at TV.

@ gfe-6
How about not being borderline rude and answer the OP's question instead? They were planning to release Dragon Tattoo as a full time movie, it was in their plan and not as some shorten version of the TV-series. The only one out of the three. But I think this is what the OP wants to know:


The "official" story:

"He directed The Girl with the Dragon Tattoo, the 2009 Swedish film based on Stieg Larsson's novel of the same title and won critical acclaim internationally. Oplev decided to not continue directing the second and third parts of the Millennium Trilogy due to time constraints. The film has broken box office records in Europe, grossing over $100 million USD."!

http://en.wikipedia.org/wiki/Niels_Arden_Oplev


This is the reason he didn't direct the sequels:

"But after the European release of something like “The Girl With the Dragon Tattoo,” the Danish director Niels Arden Oplev said, you can’t go home again. Not professionally, anyway.

“We sold three million tickets,” he said of what was the most successful European film of 2009 and one that arrives in the United States on Friday surfing the publishing tsunami of the late Swedish novelist Stieg Larsson’s series of crime novels known as the Millennium Trilogy. “If you add all of Europe, the sales are more like eight million tickets. So I just felt, I don’t want to be in Scandinavia right now. If I make a Scandinavian film, and it sells 100,000 tickets, which would still be good, then that’s a major failure for me.”
And, he said, “I’ve always had this dream of doing an English-language film.”

Before “Dragon Tattoo” even completed production in Sweden, Mr. Oplev had moved his wife, Florence Tone, and their four children from outside Copenhagen to Cranbury, N.J. “It was crazy,” he said. “Literally, the coffee cups were standing on the kitchen table in the house in Denmark. We packed two suitcases each and left the furniture. It’s typical of Florence and I to do something like that."

http://www.nytimes.com/2010/03/14/movies/14dragon.html