your in luck, i just slaved over my sisters kia optima 2004 to replace just that today. theres not really instructions but i can try and give you a break down.
first remove the top engine cover. then the heat shield on the exhaust manifold to give you working space on top. then jack up the right front side and put a jack stand under it. remove the plactic cover that is on the inner fender by the engine, make sure the tires are turned to the right. then remove the small plastic cover from under the vehicle.
now you have your working space. youll need 10mm 12mm 14mm 2x 17mm and 22mm socket along with the others in socket ,deep sockets as required. now take the upper timing cover off there is 4 10mm bolts holding it on. this will expose the cams. take your 22mm socket and rotate the engine crank shaft to top dead center, youll see both cam marks pointing up when it is correct. this is to prepare you for removing the timing belt. now start working on the a/c and p/s belt tension to remove the belt. then work on the water and alt belt tensioner to remove that belt, now that you have no belts in your way its time to move the p/s pump out of the way. youll see 4 14mm bolts two on the timing side and two on the back side one holding the oil dip stick. thius is tricky, remove the oil dip stick bolt first then rotate the oil dip stick tube toward the radiator this will give you room. now work on the bolts on the timing side. youll probly not be able to remove these to just get them loose so they slide out. next loosen the 12mm bolts on the p/s pump connecting it to the bracket you can access these by rotating the pulley. remove the one closer to the engine and then only loosen the one next to the radiator this is to to rotate the p/s to gain access and remove the last remaining 14mm bolt connected to the bracket.
move it toward the right front fender and slide the p/s resivor out to give more movement. now look for the p/s hose that travel back towrd the firewall, youll see a rubber gromet and a 10mm holding it down remove this as well to get this bulky hose out of the way. starting working on the 10mm bolts holding the water pump pulley on, this will take time and youll probly want to start shotgunning a few beers to calm yourself. now that your probly pissed and bleeding from the small space in the vehicle move on to removing the crankshaft pulley. youll need a way to hold the crank with a 22mm socket and the bolts are 12mm. now start removing the 10mm bolts holding the timing cover on. romve this cover and now you should see the timing belt and all the goodys. here comes the fun part, remove the timing belt tensioner its held by 2 12mm bolts its under the big shiny wheel toward the alternator. this will let the timing belt go and youll probly hear the cams settle so dont be alarmed.
when you remove this tensioner youll see it is hydralic, youll need to compress this slowly in a vise and line up the hole you see in the tip and in the casing of it, its very small so youll need something thats hardened and not going to bend, i used a straight part of a spring and it seemed to do just fine, needles with not work. so now that you preloaded the tensioner move on to removing the crank shaft position sensor. 2 10mm bolts. it should slide out but pay attention to how the wire is routed, this is very important the timing will destroy the wires in seconds if they are in the way.so install your sensor and route your wires.
here comes a reason to have a second person, have 2 17mm wrenchs and postion the belt over the cam gears, make sure your marks are lined up and youll have tension going both directions to hold this in place, now start routing the timing through the front past the idler and now line up the first cam gear with aluminum tab at 11 oclock i blieve, and make sure you crank is lined u with its alignment mark on the crak sensors wheel in the top left about 10 oclock. when in stalling the belt its important to check back make sure your pulling the belt through to take up all tension so it is aligned. now keep pressure on the cams, with the timing belt tensioner installed remove that little pin thats holding it and let it sit for a second as it takes up the tension, remove the 17mm wrenches and go ahead and bump the motor a couple rotations and use the wrench to find tdc again, if your timing is correct the tensioner is taking up slack then your good to go. now start installing everything backward. lower timing cover crank pulley water pump pulley, install the p/s bracket install the alt water pump belt then the a/c p/s belt. get the belts snug with the tensioner. dont forget to install the oil dip stick tube back to its lower bolt on the p/s bracket.
go ahead and give the motor a test start and see if eveything is ok, then go ahead bolt everything else down.
now assuming you recieved the p0335 error. random shut offs or doesnt start at all?
good luck and ready yourself with about 6 hours.