I'm in the midst of changing the belt and tensioner on my 2010 Rondo (90000 KM) 2.4L 4 cylinder.
I've been a heavy equipment tech for the last 20 years. Replacing the belt is not DIY friendly.
I'd recommend buying a kit on-line that includes the tensioner, upper and lower idlers and belt.
Start by chalking the rear tires, raising the front of the car off the ground and remove the passenger side front tire. Remove the splash shield.
Disconnect the battery -ve cable.
Remove the engine cover
Complete the following steps to create access to the belt, tensioner and pulleys.
Remove the 10mm nut from the A/C line restraint, forward of the frame side engine mount
Remove the 10 mm bolt from the grounding cable on the engine mount.
You need to remove the passenger side engine mount, place a block of wood on your jack and take up a small amount of the slack in the mounts.
Remove the nut on the frame side of the mount, remove the two nuts and 1 bolt from the mount on the engine.
Remove the frame engine mount base from the frame. (3 nuts)
Shown in this picture, the tensioner is above the timing mark on the engine cover, up and to the right of the crankshaft, the smallest diameter pulley.
Now, using a 17mm box wrench move the tensioner toward the rear of the car and slip the belt off. The tensioner's release is the bolt in it's pulley. The pulley is right against the frame rail, you'll only be able to use a box end wrench for access.
To remove the tenisoner you'll have to remove it's pulley - this is a left hand thread, turn clockwise to release, counter clockwise to tighten. Now remove tensioner. It's tight for access. You may wish to remove the engine side of the mount to create some extra room.
Assembly is reverse.
This is not a fun or easy job. Quite a variety of tools are required. I selected my parts from nation wide parts provider with generous warranty. I'm not paying to do this again. For what it's worth, I used a Continental belt part number 1061017 (6PK2582) and tensioner 49428. The tensioner pulley is not available in the aftermarket alone, though the bearing used in the Continental tensioner is THE EXACT same as the OEM Kia bearing. Let that sink in for a moment.