Revamping website (same domain), how do I smoothly and not lose my SEO?

Hello, I built a DIY website on wix about 4 years ago. My business ranks really well right now in SEO for various cities that I service for my service based business. I hired a guy to build me a new website and it looks amazing. He built it on Wix Studio. I am ready to try and pull the trigger on my revamped website (I still want to use the same domain names, ect). However, I am extremely worried about losing my SEO or even worse getting flagged by Google. Any advice before I proceed?