Any updates you make to page titles and meta tags can take some time to show in the Google search results.
Google's results are not a live preview of your website, but a cached copy.
In order for updates to show in the search results Google needs to re-crawl your website and they do this on their own schedule.
You can ask them to re-crawl a page that you have updated by logging in to Google Search Console and using the 'Submit to Index' functionality - https://support.google.com/webmasters/answer/6065812?hl=en
Even if you choose not to submit pages that you have changed, your updates will eventually show anyway.