How much do you change when writing fiction based on real life?

I’ve been working on a story about some things that happened to me and my friends a few years ago. It’s pretty character-driven, so I don’t know how to change people’s personalities or the events in the plot. I could change superficial things like physical appearance, the location of the story, or favorite colors and foods, but it seems like it would still be obvious who I was writing about. I wouldn’t want to hurt anyone by writing this, because some of the things in the story are kind of negative. What’s the right way to go about this?