I just have a base model ATS so I will add the parts I want as I go. The first upgrade is the Pedal Kit. You can get the kits for about $125 shipped either off eBay or from a GM dealer.
So, what is in the kit?
You get a new foot rest cover, new brake pedal cover, a accelerator pedal (with controller - drive by wire) and some crappy instructions.
Before
After
Tools
1) Small flat blade screw driver
2) #4 metric allen wrench
3) a curved tool to help put on the brake pedal cover.
How To
Foot Rest
Using the small flat blade screw driver remove the retaining clip at the top of the foot rest. Once the clip is removed push down on the tab and remove the cover. The kit provides a new lower connection plate and retaining clip. But, they are the same parts as what is already installed.
Next take the new foot rest cover slide on the lower connection plate, making sure the bottom is in the mounting slot.
Now push it down until the catch at the top snaps in place. Replace the retaining clip and your done. It takes all of 5 mins to install.
Brake Pedal
Remove the old brake pedal cover... It just pulls off. Now the fun begins. It took me at least 30 mins to get this sucker on. Why? For one thing it is not as flexible as the one you took off. Secondly you have stretch the rubber over the brake pedal. I started with on the accelerator pedal side and worked my way around the bottom to the top. You will need some sort of small curved tool to assist in getting the rubber over the pedal.
Accelerator Pedal
With the small screw driver remove the rubber plug the covers the hold down bolt. Next use the #4 metric allen wrench to remove the hold down bolt. Now pull back on the pedal assembly to release it from the floor. Disconnect the cable from the control box by unlocking the red release clip on the plug.
Swap pedal assemblies, install cable connection and slide the locking clip into position. Now slide the assembly back into the floor, install the retaining bolt and the rubber plug.
Start the car and check out the new parts.