Hi Rubantin To make sitewide changes are you using an HTML editor? If so, which one? For instance are you using DreamWeaver or Expression Web or something like that?
Hi Rubantin What you need to do is make sure you have defined the site in Dreamweaver as outlined here - https://www.ecommercetemplates.com/tutorials/default.asp#dwdefine
Then from within Dreamweaver open the file main.dwt in the Templates folder, and any changes you make to that file will update all your other pages when you save it. Then just upload the updated pages to the server