How to transfer files to your Web server
Although not specific to WordPress, the most common means of transferring files to a Web server is by using a file manager provided by your host or via a FTP Client.
The most common of the host provided means of transferring files is via cPanel which is a simple to use file transfer service. The advantage of using cPanel rather than a FTP client is that there is no local computer installation required for cPanel.
For anyone requiring transferring files on a regular basis then it will be beneficial to install and use FTP client software. Some of the best FTP client software is free to download, install and use such as the very popular Filezilla. There are also free to use FTP clients that integrate into Internet Browsers; FireFTP is a free add-on for the Firefox browser.
For self-hosted WordPress (i.e. wordpress.org) use it is best to use an FTP client due to their faster speeds and better fault tolerance.