Default templates will be overwritten with new updates, do not customize the default templates, instead create a new folder in the templates folder and copy the default template files you wish to use to the newly created folder. Now customize to your hearts content in your personalized template folder and activate it by choosing it in the template selector setting in site settings. This step will prevent having your customizations overwritten during upgrades.
If your template folder is not showing in site settings after creating the folder and copying the files you may need to either refresh the page or verify you created the new folder inside of the templates folder.
Default templates are licensed for the domain they are included with only and clients may use them however they wish on their licensed domain. Clients of Aurora Coderz may not sell Aurora Coderz default templates or derivatives based on Aurora Coderz default templates.