Need help to upgrade directory responsive theme from 4.4 to 5.4

Guys….

I need to upgrade from my current directory theme 4.4 to 5.4 and I have very limited experience with web stuff…

I checked under WordPress// Dashboard// updates…. I can see updates for plugins and only one theme which is the “Twenty Eleven” theme… a screen shot attached

I need to assure that I will never lose any of the below…

I am using a child theme and just did the below changes…

• Changed colors
• Changed menus…added items and removed some
• Removed all packages and listing options (just kept the Free option)
• Used some of the available Widgets
• very few plugins activated… Shrink the Web and WordPress SEO
• Also have 1600 listings
Thanks