Unless you have written permission to remake it you are you not allowed to do this unless you only use it yourself and don’t share it with anybody else.
Unless it was open source, then I think you are allowed to do it.
However, having access to the code does not mean that it is open source. Please research if it is open source or not.
So I have a copy of the free to use Warzone2100 and have been toying around with the idea of bringing it to UE4 and updating it to UE4. Now I have access to the source code of the game, is it just a simple copy/paste matter? or will I need to reprogram from scratch? I’m fairly new at this, and wish to use this kind of as a learning experiment. Can anyone help?