Attack on Titan names are somewhat flavored German, so if you can pronounce “Hange” like the Germans would (“Hahnj”? It’s the German word for “hang.”), that would probably be correct.
Though if you want to pronounce it like it’s spelled in katakana (Han-ji), that would probably be correct too! There’s a lot of room for interpretation on this one, because while there are certain names that we know for sure*, Hange isn’t so clear cut. Basically, Japanese gets kinda weird when they try to write German names in katakana (I had a friend whose last name “Ziegler” became “Jiiguraa” to our Japanese teacher. xD), so we made our best educated guess. Here are some tweets from the editor about that (1 2).
*Like Levi. It’s on the manga-ka’s blog, so sorry to all you Ravioli fans. ;P He’s named after the kid preacher from Jesus Camp.