In the comic book version of X-Men: Days of Future Past, Kitty Pryde was the character sent back in time to set things right for the future. In the movie adaptation, Wolverine is the one sent back in time to do it. In a recent interview with Total Film, writer Simon Kinberg explains why they made the change. Here's what he said,
"We made the decision for a lot of reasons, some of them obvious and some of them more nuanced, to make it Wolverine who goes back in time. One reason is that he's the protagonist of the franchise, and probably the most beloved character to a mass audience. Probably the bigger reason is that when we started thinking about the logistical realities of Kitty's consciousness being sent back in time, to her younger self, as opposed to her physical body being sent back..it was impossible. Obviously in the book it's Kitty..but you're talking about an actress (Ellen Page) who, in the age of Michael Fassbender and James McAvoy, would have been negative 20 years old. So we started thinking again, and the first reflex response to that was a character who doesn't age. Wolverine is the only character who would looks the same in 1973 as he does in the future."
That makes complete sense to me. I haven't really seen anyone complain about the change, but just in case you were wondering why they did it... there it is!
X-Men: Days of Future Past opens in theaters on May 23rd, 2014. You can watch the trailer here if you want to remind you of the awesomeness that awaits.