How do you talk a dealer down on a new car?

im trying to trade my 2010 kia forte koup premium package for a 2011 kia serento because im expecting and my boyfriend has two kids and we have two dogs... there just isnt enough room. im trying to talk my sales man down. i havent went to the dealership yet though. if i have to settle for a 2010 i will since its the end of the year and i know they need to get rid of that model