When you FTP into your store's FTP server, there will be certain files and folders which you will not be able to access. For example, the various ASP files that make up the core of your store's software as well as the web/admin folder.
These files and folders contain the shopping cart source code, which we maintain and for this reason we do not allow you to make changes to them.
Another folder you can access but not write to is the Common folder found in web/assets/templates. This folder contains all of the global HTML templates used on your Shift4Shop store. We specifically maintain this folder, so you do not have access to write to it, but you can copy templates from it and place them onto your individual theme folder (i.e. web/assets/templates/v30014 if you are using that particular theme).