When you wish to make changes to your website you will need to access the server where your website files live.
This is called a Host Server. Usually websites are hosted on servers owned by third party specialist hosting companies. For a small monthly fee you can rent space on these hosting company servers to house your website. These servers are on 24/7 and have fixed IP addresses so your website is always accessible.
To access your files over the internet at any time you need to use a FTP client. This is a piece of software you install on your computer. The most popular FTP client is called Filezilla (pictured left) and it is completely free.
You can click on this link to go to the website where you can download the Filezilla client.
Here is a brilliant video showing you how to install, set up and use Filezilla.