Ahh. If you don't find any button to update the theme automatically, so you can do it manually.
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So please make sure that you do not change or custom anything to the Main theme. If not, all your changes will be lost after you update the theme to the new version. And now, pls follow these steps to update manually the theme:
Step 1: Go to Appearance >> Themes > Activate the default theme of WP
Step 2: Delete the Current Boutique theme on your site.
Step 3: After downloading the new theme package on TF, pls extract and find the theme zip file => go to Appearance >> Themes >> Add new and upload the new theme package version to your site.
Step 4: Await a bit until it's finished and activate the theme. Then your site will be in the latest version of this theme.
If you need to ask anything, please let me know.
Thank you!