The movie's release date has changed from June 29th, 2012 to March 29th, 2013 in order to convert the film into 3D.
Part of this has to do with helping the film perform better internationally, but some of it may also have to do with the fact that G.I. Joe 2 would have had to go up against The Amazing Spider-Man, both of which would've had to share a very similar audience.
I'm very sad to hear that we will have to wait an entire year for GI Joe Retaliation. For now, we can just enjoy the trailers, posters, and movie stills as we wait for the film's release next March.