Your personal feelings about people, situations, things, experiences, etc. are all based on your thoughts. This might be incredibly obvious to some but I really want you to sit in that for a second. Your feelings are based on your thoughts. That makes it obvious, then, that if you can change your thoughts; you can change your feelings. It doesn't, however, work the other way around, you can't change your feelings first. So, here's how to change your feelings, make a new truth for yourself.
Let's say you feel angry towards a family member. You can't change that feeling but you can change the thought behind that feeling.
Before you can do that though you have to really understand the thought, not the surface thoughts that are meant to distract you, the true, deep thought. The one that might hurt to realize or might struggle coming out. That's the thought you have to really understand. So, if you're looking to change a feeling look deep within yourself, sit with the feeling for awhile and figure out what the true thought is, then rewrite a different thought. Instead of "I'm angry because..." you could say "I was hurt but I'm recovering" or "I was angry but I'm moving on"