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1.  Here’s the link to the training documentation on the Theme Builder we have used on your site, it’s called ‘Divi’.  https://www.elegantthemes.com/documentation/divi/
2.  Here’s where to find the training videos inside your WordPress site:
Divi Training - Where to locate inside WordPress.png
3.  Below is a screenshot of the different training modules.  
We recommend you do the ‘Divi Basics’ and ‘Divi Modules’ at least.
You may find you can easily make updates just from trying these ones.