I have a 1997 Limited and Im unsure as to which tire size to go with. The original tires were P235/75R15 but the current tires are 30x9.50R15 so I'm wondering what the difference is between the two. I'm looking to buy bigger tires but I'm mostly concerned with extra height not width but I have no idea which size I should use. I'm guessing 31x10.50R15 or P265/75R15 but I honestly don't know if these are the ones to use or if they will fit my stock rims. Please help because I have to ship the tires to my location at a cost of $250 Cdn so I can't afford to try different sizes. Thanks.

 

There are tire size calculators out there. Here are the basics:
metric tire sizes work like this
1st number (235) = width of tire tread in mm.
2nd number (75) = height profile of tire (from rim to tread) as percentage of tread width (235 * 75% = ~80 mm)
3rd number (15) = rim diameter in inches.

tire sizes in English units work like this:
1st number (30) = overall tire dameter in inches.
2nd number (9.50) = width of tire tread in inches.
3rd number (15) = rim diameter in inches.

The "R" indicates a radial tires as opposed to bias ply tires, "P" stand for passenger tire and is an indication of the quantity and stiffness of the rubber, and "LT" stands for "light truck" tire and has more rubber than a "P" rated tire. A 235/75R15 tire is approximately equivalent to 29X9.50R15, so it's about 1 in shorter than the 30X9.50R15 that you have now.