A friend of mine has a Wordpress website that's really old and uses a really old Wordpress theme.
I am building her a new site from scratch with a new, modern Wordpress theme.
Now I understand that this can be done simply by applying a new theme on the existing website but I think this completely jumbles up the website and the content is all over the place. It will take time for me to re-organize the information and we cannot afford for the website to be down or under maintenance for such a long period.
What is the best way to smoothly transition?