Once the metal piece is out of the way, you should have easy access to the two 10mm bolts housing the thermostat.
Accessing the thermostat (10mm socket)
Use a 10mm socket and extension to take out these two bolts. They are both grade 8 and around 4 inches long, so take your take.
Checking out the thermostat and replacing it (Thermosat and 0-ring)
*NOTE* Some fluid will still be in this, so be cautious when unbolting. I didnt do a write up on the full flush, so proceed at your own risk.
Once the top is removed, you should see your thermostat.
Use a pair of pliers to remove the theromstat incase the coolant is still hot. You can use a ligther to check the thermostat and sometimes get them to work, but for 20 bucks, I decided to completely replace mine.
I used a rag with some water to clean up the edges and make for a nice tight seal, so I suggest doing this with all your hoses and connections. My buddies took my truck "4 wheeling" so I had quite a hard time getting everything clean.
Old vs New
Remove the old 0-ring , mine was stuck to the end of the hose.
Place your new thermostat in, and put the 0-ring on top of it. The fitting at the end of the hose will seal around this, so dont worry.