Need help hex editing an unreal engine game file Thread

Hey guys, I'm new here. I signed up because I needed help hex editing a .u file. If someone would like to help me, it would be really appreciated. Basically, all I want to do is replace an existing class, with another. I know the basics of hex editing so I'm not new to that, don't worry :p
I got everything you need, I just need someone to help me with replacing hexes with others cause everytime I try something, the game crashes. Thanks