I can't get my serpentine belt tight. Anyone have link to replace? Engine 3.4. on 2002 Chevrolet Monte Carlo

When I tighten the tensioner it seems like it is starting to get tight then it gets real loose again.
Is it hard to replace the Tensioner if its loose?
FYI I am not mechanically inclined.
Thanks for any response.

Asked by for the 2002 Chevrolet Monte Carlo
sounds like the tensioner but if you are not mechanically inclined I would take it to a mechanic