First download FTP software, please see https://www.versio.eu/articles/262-what-ftp-software-do-you-recommend. Below you'll find information on how to work with FileZilla.
Step 1
Open your FTP software and provide you FTP host, user name and password. You have received this information by e-mail. If you lost them, please see https://www.versio.eu/articles/265-i-have-lost-my-hosting-account-details-directadminftp-what-should-i-do
Step 2
You are presented with two screens. The left screen is your own computer, the right screen is your webhosting account. Double click "Domains" in the right screen.
Step 3
In the right screen, double click the domain name to which you wish to upload.
Step 4
Double click "public_html".
Step 5
In the left screen, you can navigate to a folder on your own computer. You can update files and folders by dragging them to the right screen.
