I'm doing the exact same, u tried to get into me3.8 when I had my golf and was pretty difficult. Then started looking into me7.5 which I have to admit is a lot easier when you have full definition files easily available to identify maps etc. you need to read up on what maps need to be changed and why changing them has an effect and what effect it has on the engine. Pointless just finding a 'boost' (put lightly) and upping the whole table bus set % as it doesn't work like that.
Google the s4 tuning wiki and read that, there's a few guides out there aswell that cover the basics.
It's far from easy, I've been looking on and off for a while and only just got to understand load and boost maps on a basic level.
Finding someone that has the time to teach you is the issue, luckily I have a golden opportunity to spend time at a reputable company showing me how it's done etc. rare as it comes!