How do i configure PS 1.6 front page

[LyHua]

Hi, i'm currently a uni student. I have had experience working and creating a website for my own before. A week ago my uncle ask me to help him redecorate his prestoshop website and only giving me access to the back office. The only way after i research that can configure the web is by editing and configure the already implement or template modules which are the theme configurator and etc,... But i want to configure the web file myself, the css stuff but i don't know how to ask my uncle since he's not well verse in these kind of things. I believe that he picked the hosted offer when he create his web back in 2017. On the back office it said the server is hosted on Linux the server software is Apache. If anyone has experience with PS 1.6 can you tell me how did you hook the website up and where is the source code for the web locate at so that it is easier for me to ask my uncle