You can read over here for for data compression information
https://encode.ru/forums/2-Data-Compression
Not easy to say for an unknowing person like you.
Also you can grab this
http://fileforums.com/showthread.php?t=99270 to check game files.
To start, it's good just to try different compressions on different files, then you will learn much more about it just from trying it out.