In order to upload your files, you can use the control panel's built-in file manager: just click on the Files tab and then on the Upload button. Additionally, you can use any FTP client such as FileZilla, Cyberduck or WinSCP. If one of your files is larger than 200MB and/or your connection is slow, we strongly advise you to use an FTP client.
You will find all FTP login details by clicking on the control panel's Settings tab (then look under SFTP Details). In case you have set a default FTP client on your computer, you can simply click on Launch SFTP. If that doesn't work, just copy all data from the Server Address and Username fields straight into your FTP client's connection settings (exactly as they are).