There are 2 different 3L engines offered, so you will need to take a look at diagrams to see which one is yours:
Fig. Serpentine accessory drive belt routing-3.0L (VIN U) engine
Fig. Serpentine accessory drive belt routing-3.0L (VIN S) engine
Attach a 15mm socket or wrench to the bolt attaching the tensioner pulley. On all 3.0L (OHV) engines, rotate the drive belt tensioner clockwise to relieve belt tension and slide the belt off the pulleys. On 3.0L (DOHC) engines, rotate the tensioner counterclockwise to relieve belt tension and slide the belt off the pulleys.
Fig. Rotate the belt tensioner and . . .
Fig. . . . remove the belt from around one of the pulleys to remove the belt
Fig. A very useful tool kit is available to use for releasing the spring loaded belt tensioner
I will add that the above tool while not required is helpful as it gives you added leverage and reach.
Also, while directions dont say to do this, if you have large hands or arms, you will find removing the right tire and inner wheel splash shield makes it easier to route the new belt.
What I do on installing the new belt is route it around every pulley(including belt tensioner), except the top most pulley. Then with one hand maintaining tension on belt so it doesnt slip off any pulley, I use my other hand to rotate tensioner to relieve tension and the slip belt over top most pulley, and then release tension on tensioner