How to change sepertin velt

Hello, Those should be the hydraulic tensioners. On the front bottom of the engine, right above the oil pan, release tension on that tensioner by loosening the two bolts that hold it in place slightly. You can now move the tensioner by turning the large nut on that little bracket. The other one is similar, but the tensioner is mounted up to the right as you are looking at the engine. Once you release the bolt that keeps it in place, you can turn it by the large but. Two pulleys will move.