im 16 and brought my first jeep a couple months ago and i brought a 95 jeep yj with a 4 banger and a 4inch lift with 33's.  i am quickly learning that the 4 banger is hurting when i go off roading.  I am wondering if anyone has ever done a engine swap with a cherokee engine the 4.0 straight 6 into a yj?  and how mony money will it cost to do this? and will i ahve to swap out the rest of the drivetrain?  or would it be easiert to just mod my 4banger so it will have more horsepower?  

it's not the hp, it's the gear ratio. instead of trying to build up the engine, try lower axle gears or maybe even 4 to 1 low range t-case gears. i guess i'm assuming you're definition of going offroad to be trail rides or rock crawling. if you're mud racing or blasting the dunes, you never should have bought a 4 cyl in the first place. 4 cyl gets it done on the trails with the right gearing. look at all the sami's on the trails. those engines have about as much hp as my lawnmower.  

what gear ratio do u think i should use  

Id say 4.56 or 4.88 but check randys ring and pinion they will tell you how much works best and they have the math to figure it out on the web.  

If you are concerned about offroading in your jeep. I would change the gear ratios before i would worry about engine swaps.  I am 17 and have a '95 YJ. I have 4.56 gears with my four banger and 31's with 2"body lift.  The lowering of the gears allows me to jeep any where.  So lower the gears then if thats not enough then swap for a I6 out of a YJ.  You can take computers and all and it mounts to your Jeep.