Editors sometimes suggest drastic changes--removing characters, deleting scenes. Consider your editor's notes carefully, but don't assume they're getting it right the first time either. Think about why you wrote it the way you did in the first place. If you think the editor's ideas improve on yours, take the advice. If you have doubts about it, talk to the editor. Ask them about their suggestions. We never do things without a reason and unearthing that reason could be the key to improving your manuscript. Sometimes what one might think is the problem is actually just a symptom of a different problem. To dig deep enough, you need to express your hopes for a scene to your editor.
On the flip side, be careful not to just be blindly defending your work. Instead of arguing with your editor or beta reader, ask them about their response. "Why?" is always a good place to start.
In short, don't assume anyone is perfectly correct (including yourself). If you have questions about why they felt a certain way or suggested a specific edit, always ask. That's how you'll discover the real problems and the real solutions for creating your masterpiece.