Use CuteFTP or FreeFTP (easy to use)- etc to connect to your website with correct username/password.
Mine then shows
mail/
web/
Double click on web/ (or equivalent)
Locate your index page on the h/d - index.htm or index.html - one site I have uses .htm & the other .html.
Then drag & drop , or highlight file & click on up arrow.
You will see the file transferring. When done disconnect.
Boot browser & try. Should be ok.