To upload files to your web site you'll either need an FTP program that will log you in to your control panel and transfer the files that way, or you may do so by going directly to your control panel yourself.
To visit your control panel simply visit your web sites url (web address) with "cpanel" on the end of the url.
For example if your domain was mywebsite.com, then you would go to http://mywebsite/cpanel
Once your inside your Control Panel
Once your inside your control panel to upload your files, you'll need to click on the "File Manager" icon.
The screen that follows is much like Windows Explorer, with directories on the left and files on the right.
ALL FILES FOR YOUR SITE MUST be uploaded to your public_html directory.
Double click the public_html directory which opens it.
Everything in your public_html directory should be inside of another subdirectory, other then a few system files used by your site.
For example it is a bad idea, and very poor house keeping to upload images and media files directly into your public_html directory. There is an "images" for your images, and other directories can easily be created by clicking on "create folder".
Once you are inside the directory you want to upload the files to, click the "Upload" icon near the top and you will be prompted with an upload panel to retrieve your files from your computer.