Widen Page Width

I updated my website to the latest version of WordPress. Therefore, I lost a lot of the customization of my site. One major problem is I need to widen my site. I would like to make it full screen. It is making my header image pixelated and stretched awkwardly. I am very new at wordpress. I found the full width template page in editor, but have no idea what to do next or how to implement it. Am I on the right track? What should I do?

Also, I would love to get rid of the bar underneath the navigation bar that says what page you are currently on and any parent pages that it may have. Any suggestions?

Here is the link to the site.

Thank you