Latitude D830 Resolution

Hi, I just noticed something I never knew of. I was reading dells site and it says, Wxga+ = Resolution of 1440x900 .. well I bought my computer through my school and it said, Display: 15.4" WXGA+ (Wide) .. When I go to properties to try and change my resolution the max I can have is 1280x800 .. how can I make it this 1440x900 if WXGA+ is the more enhanced version which is 1440x900 , please help?