Hello,
1/ It is already <h1>
https://prnt.sc/-Qxy-kJbIczF
2/ etheme_product_cats function you can find in xstore/framework/woo.php file, edit it via functions.php file of your child theme, and use CSS code to change styling if this will be needed.
3/ etheme_single_product_brands function you can find in woo.php file
Please note that additional customization in files is outside the scope of our basic support.
Regards