Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - General Remove Classic Files

I have 120GB SSD too. You can delete the old "Data" folder (not "DefEd") to remove 30+GB of the old game. You just won't be able to play the old version.

See : Game taking up nearly 70GB of space?

Alternatively (if you have an external HDD) you can install it there and then just copy what you want to your SSD. Then if you wanted to play the old version you could delete "defed" from your SSD and copy back "data".