Tire Size on 6*6

[Backwater Retrievers]

I am new to the forum and I've enjoyed learning a little more about my ranger from it.

I've got an 03' Ranger Six Wheeler and I am needing to put new tires on it. I'm still running the factory tires but it is well past the time to replace them. I am pretty fond of the itp mudlites but I am needing to know what size tire I should go with and can go with? I think it has 25's on the front and 26's on the back but I am wanting to go a little bigger if I can but do not want to put too much tire that it bogs the machine down(500cc). I use the machine for play but 99% of the time for hauling hunters in some nasty mud. I have very impressed with it and that was with bald tires so I'm sure I will be in hog heaven with some tennis shoes. Just need some suggestions on what ya'll think. The machine also has a 2 inch lift but I am unsure about the tires because of how close the two back tires are together.

Thanks for all the help.