My V8 Soarer has smaller brakes compared to the TT, so I decided to upgrade to the TT front brakes.  I bought a set second hand, had the rotors machined then fitted them along with some Ferodo DS2500 brake pads.  In retrospect, machining was a bad idea as the disks weren't buckled so I was just wasting rotor thickness which legally has to be a minimum of 30 mm.  To make matters worse, I had them skimmed twice as I wasn't happy with the first job, I wanted to have nice smooth rotors. I know better now.

Fitting new pads to the skimmed rotors was also a bad idea I have since found out, much better to fit new pads to old rotors and vice versa. The pads transfer a thin coating of material onto the rotors for best braking and skimming removed this coating.

When my rotors started to cause a shudder at high speeds, I didn't have enough thickness left to have them machined again, if I hadn't machined them  the first time for no good reason, I could still be using them. I am not sure why the disks started to buckle, it was just the drivers side one that went.  It may have been due to incorrect bedding in procedure or possibly it was buckled when I bought it. Machining can release the stress in the metal allowing it to conform back to the original buckled shape again, as I noticed a very slight tremor right from the start which got progressively worse. I was hoping it would go away as the pads settled in, but it didn't.

I then bought some D.B.A. 4000 slotted front Rotors for $450 the set which I am so far happy with.  The passengers front rotor has already got quite scoured due to running out of brake pad during a track day, but I am not going to bother getting them skimmed as the new pads will quickly conform to the shape of the ridges.  Theorists suggest machining the rotors every time you change the pads, but if you do track days you can end up changing the pads pretty often and there is no need to be replacing your rotors because you have skimmed them too often.

Changing the rotors is a simple job in itself, but while you are there, check the pads and flush the brake fluid if it hasn't been done recently.

Undo the two bolts that hold the entire calliper assembly, lift the calliper complete away and sit it on an upturned bucket.  Don't leave it hanging on the brake hose.

The rotors should come off easily, but if they are seized on, there are two threaded holes (only one visible above) closest to the hub that you can put bolts into and do up evenly to pry the rotor off. You might also try spraying some WD40 or equivalent into the holes and letting it sit for a few hours first.  Try to avoid using a hammer, at least start with a rubber mallet if you have to, or use a block of wood if you have to use a real hammer.    A car jack has also been used to get the rotors loose, but be extremely careful what you brace the jack against.

As the new rotor will be a bit thicker then the old one, you will need to press the pistons back into the calliper a bit.  I use a thin G clamp and an old brake pad to do this. Apply the pressure evenly so both pistons slide back together.

Fit the new rotor on, replace the calliper assembly and make sure the bolts are done up really tight.    Really really tight, use a long breaker bar, not a ratchet.

As with all brake work, test the brakes for feel while the car is parked, then test them gently when the car is moving.  New rotors need bedding in, both to acquire a coating of pad material, and to get "cooked" gently through heat cycles.

Go for a long suburban drive to allow them to warm up gently, then on a safe stretch of road, start using firmer pressure from e.g. 60 kph down to 10 kph, then from 80 kph etc.   Avoid complete stops as that will cause uneven cooling that can warp the rotors.   Take a long drive home again using the brakes very gently to allow them to cool properly before parking.

The longer you take to season the rotors the better, so don't just rush out and start cooking them.