The video shows you how to upload the wordpress zip file to public_html and extract it. It will extract into a directory called wordpress.
If you already have a wordpress install in public_html called wordpress, then simply use the Cpanel file manager to create a new directory in public_html and name it anything--let's say WP-TEMP for example. Then upload the wordpress zip file into WP-TEMP and extract it there. Once it's extracted into the directory, you will have public_html/WP-TEMP/wordpress -- now, just rename that wordpress directory to something else -- blog, for example -- and then, move it out to public_html. Then you will have your new source code in public_html/blog and your other install will be in public_html/wordpress.
Just follow the rest of the video from there.
Note: If you want to use the same database your other blog is using, then see the following video for installing multiple blogs using a single database.
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