You didn't state what year your Sportage is so I'll assume it's a 1996 or newer with the DOHC engine. 1995 Sportages could have either the SOHC engine or the DOHC engine.
The DOHC engine is a "non-interference" design which means the engine will not be damaged if the timing belt breaks. The SOHC engine is supposedly an "interference" design but we've have a few folks drop in who busted the belt but got lucky and installed a new one and were good to go.
A sure bet that the belt is broken: Does the engine crank ALOT faster than it used to? If yes, it's broke. If no, your problem is something else.
You can find instructions for changing the timing belt at
http://www.kiatechinfo.com. But the instructions can be a little confusing and are incomplete. For example, the entire clutch fan mount must be removed as well as the cooling system drained and the thermostat housing removed. The radiator can stay in place but it's easier if you remove it.
One other "gotcha". Crank pulley removal. There are 6 - 10 mm bolts that hold it in place. You do NOT need to remove the 22 mm center bolt. If the crank pulley doesn't come off tap it with a block of wood and a hammer. It should drop off.
If you have high mileage (say greater than 80K miles or so) you should consider doing the water pump too if you need to replace the belt. If you are going to replace it get a GENUINE Kia water pump from a dealer. Don't go aftermarket. Aftermarket water pumps may in fact be for the SOHC engine and it will fit but destroy the new timing belt.
That's about it. If you need more assistance post back. I've done the timing belt and water pump myself so I can talk you thru any problems.