Pretty simple. I did mine, but it's a 4.0L, but am very sure it's nearly exact replacement procedure on your 3.0L.
1. take your belt loose.
2. there's a bolt(takes a 13mm?) that goes through the tensioner and into the block, remove that bolt.
3. remove the tensioner.
4. install new tensioner. On mine there's a locating pin that locates into a hole in the block to correctly position thte tensioner, make sure you get it in the correct hole.
5. thread in bolt into block. Tighten bolt. I don't know ft/lb specs on it. Just tighten it til it's tight.
6. install belt.
Have you looked at a Gatorback belt? They are AWESOME and QUIET!!
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.