Don't know about your particular engine, but I've replaced a number of tensioners.
Most tensioners have a fitting of some sort, which allows you to put on a socket or square drive on it and get leverage over the spring. You can also buy tensioner tools at autoparts store, which are basically just long breaker bars with couple different generic fittings. If by an unlikely chance that it doesn't have a fitting, then you just use a pry bar, being careful not to damage any pulleys.
Take the tension off the belt, remove the belt, and let the tensioner out. They'll be a couple bolts holding the tensioner on, remove those and put on the new tensioner.
I always put on a new belt, since belts are cheap and the you've already done the hardpart. Make sure the belt/grooves are correct on all of the pulleys.
Example:
https://www.oreillyauto.com/detail/r.../67061/4700272
Make sure you make a drawing of the belt path before you start. It can be a 15 minute job on a car. On an RV with limited access, and sometimes working on your back, it can be a PITA.