For most people, the timing chain tensioner gets replaced when the car rattles. I've made a habit of changing it every 30,000mi. (probably unnecessary)
The change is very easy. stand in front of the car and open the hood. If you look to the left side of the engine, about 1/2 way down the side of the block (pretty much right behind the radiator resevoir) there will be an aluminum 'knob' of sorts. That's the tensioner. Unscrew it and feed the new one in. If your tensioner has a tab on the internal portion of it, you'll need to make sure that lines up with the tensioner rod inside the block. If not, put the new one in and tighten it down.
It took me about 15 minutes to change this part, and it only cost me about $30.
Hope this helps!