Need you're help on learning how to tune my cars(Chevrolet an VW)

[Alexaxl32]

Hello guys.I'm new in this forum(like a couple of hours) and i'm sorry in advance if i'm posting this in the wrong section.
Long story short,i have 4 cars(3 are my cars and 1 is owned by my dad)
So the cars are:
1.VW Golf MK4 1.9 TDI ALH with 90 hp(at least new and 250k km on the clock)also my daily driver.
2.VW Passat B5.5 ARL(cosmetic mods and upgraded brakes with 100k km),but in the end it will get more work into,when i have the money
3.Chevrolet Aveo 2012 1.2 STEC-II with 86hp and 43k km
4.Audi A6 2012 2.0TDI quattro(the audi is owned by my father,not really that keen on modifying it)
But 1,2,3 are mine,and i would like to learn how to tune then,by raising HP and torque or by raising fuel economy(i don't think that Aveo has much to give but who know)
Now,i have heard of Winols and ECM TITANIUM and VAGSiute etc.but i need you're help with them to understand how they work,what to buy(in terms of tools\gadgets) to modify my ecu(or maps\dumps)and how to apply it.
I'm a fast learner so if you can please hepl me i would be thankfull.
Thank you for you're time.
Have a good day