I am really new to this and would like to learn I have a 2002 seat leon 1.8 20v turbo, I am looking to remap it and learn how to understand in vagedc the main difference between standard and a remap file.

Is it easy to load new file to ecu ?

It's quite difficult, but not impossible. First you need to understand very well functioning engine, and then go to the next step.
On YouTube videos, serch vagecu.... are most suggestive.
Then the next step, acquiring tools