So here I will give you the structure to update the Main theme
Please make sure that you have no customized files on the Parent theme. If you customized on this, after updating, all customized files will be lost
Step 1: Backup your site( Include codes + Database)
Step 2: From the dashboard >> Appearance >> Theme, you need to activate the default template( Ex; Twenty Seventeen theme)
Step 3: Click on Boutique theme and then click Delete( look down in the right). NOTE: DO NOT delete the Child theme
Step 4: Return the Appearance menus choose Theme >> Add New >> choose your latest theme version >> Install
Step 5: If there are any required plugins that need to re-activate, pleas activate all
Please do it and let me know.