For your Skoda and other Volkswagen Audio Group (VAG) vehicles probably the simplest way is to use something like OBDEleven, this uses what they term "One-Click-Apps" to update the necessary coding in the car's control systems for enabling/disabling/configuring various features. If you click on the individual "apps" for you car it will say what hardware (if any) is required.
Of course even if you do need some additional hardware there can still be savings to be made over paying the dealer to retrofit since you can have the kit fitted independently and use the OBD-II functionality to enable the new hardware.
The question of how you tell if you've got the necessary hardware is a little more complicated. A full scan using the OBDEleven app should provide a lot of information regarding the installed control units etc and some of the hardware is easy to check for visually but the only fool-proof way to be sure is to try enabling the feature and see if it works as intended.
There may be more you can enable through software than just what is described on the app list however. This is done through a process referred to as "long coding" (which is what the so-called "apps" do underneath) and you can find more info on what can an can't be done usually on manufacturer-specific forums.
To do the "long coding" process you need a system that supports doing that functionality - in the VAG world this means something either like OBDEleven (which supports when you have a "Pro" subscription) or VCDS, neither are free of course and both are notably more expensive than a simple ELM327-style OBD-II reader - precisely because they offer this extended level of functionality.
