Think the brake and clutch are straight swap, but the accelerator may need modding. There is/was a thread on the forum a while back posted by a lad called stapo, sure someone will know whom i'm on about. He did the RS4 pedal thing with his a4. Looked the ******, but think he's sold it now. Try doing a search mara.
You just pull the existing rubber pedals off, might need warming up though cos they can be a nightmare, heat the rubber on the rs4 pedals and slot them on. There is a way of getting them on i think i started at the bottom of the pedal got that in place and then worked it up to the top. Have you got the footrest, that simply just clips on and screws in. When i did mine the foot rest, clutch and brake were really easy it was the accelerator pedal that took a bit of brute force and alot of swearing lol.
once you've got the old ones off, apply copious amounts of hairspray to the pedals before fitting the new ones. This lubricates the pedal (allowing easier fitting of the new ones) and then drys to stick them in place with no harmful effect on the rubber, paint or metal.
as above: straight swap, no modding, the old ones can be pried off pretty easily (once warmed up) and the new ones should be straight forward (with a bit of sweating and swearing) to slot on:but as mentioned already; lots of hairspray and pre-soak in warm water and have a hairdryer ready to run in the footwell too, to warm them up a bit more... only things I'd add is you need a nice collection of old (smooth) flat head screw-drivers and make sure you're comfortable on your knees (cushion, etc)... I used a small set of bike tyre repair "paddles" (that you use for removing tyres)... which limits the chance of nicking the rubber because you will need to be very first with them.
I've posted the times before, but it was something like 1mins for the footrest, 15mins for the clutch, 10mins for the brake and then about an hour for the accellerator, but then I didn't start the pre-warming and lubricants, etc PROPERLY until about 30-40mins into doing the accelerator.
I got a secondhand pristine set off someone on here for half price a while back. Took some effort to get on and I put a crack in the flat bit of the clutch pedal itself - I hadn't realised the actual pedal was plastic and didn't appreciate that my efforts to get the cover on could snap anything! All is fine because once the replacement pedal was on it gave it solidity. Some of the advice above about heating and using hairspray, etc might just make the difference!