well you shouldnt. with some quick math the 225 tire has a 24.08" height and the 235 tire has a 24.4" height. now i know somebody is going to say that within 3 or so % of each other is ok. you CAN put them on but it will cut the life of your center diff down an unknown amount. i would try to get tires that are the same height.
the math: section width = W, aspect ratio = A, rim size = R
((W*A)/25.4)*2+R = tire height
tire manufacturers will also have all their tires specs on their website so you can compare sizes.