tldr; Can i modify Flare engine and use it for my game (f2p or not) 

That may be kinda silly question, but english isn't my first language and im afraid that i could missunderstand something. (Obviously) Im going to make a RPG game (as a hobby/spare time project). I found flare engine site and it looks like its almost perfect tailored to my needs, but i'd like to make some minor (or even major) changes to it.

Am I allowed to do this? I don't know if Its going to be p2p, f2p or if i ever publish it (but i hope so :P) but i want to clarify this before i start working on it.