Ash here from the Shopify team. Welcome to the Shopify Community!
Thank you for reaching out with your question. I'm happy to help. I understand you're trying to change your meta title and meta description, but these settings don't appear to be updating. May I ask where you're still seeing the old meta title and meta description after updating these fields and saving the new content? Please take some screenshots of the current meta title and meta description in your Online Store> Preferences, as well as where the old content is still showing to help me understand the problem.
Also, I see you mention the look of the site isn't changing when you change these settings. May I ask what visual changes you were expecting? The meta title and meta description of your site control what people see in the search engine listing preview of your site, but wouldn't actually change the look of your site. If you have some specific changes you're looking to make on your site, let me know and we can look into implementing those!