Before you install vBulletin, allow me to warn you about our policy here regarding commercial scripts. The script you have must be bought and paid for from
http://www.vbulletin.com/, and the license on the vBulletin install must be valid. If the forum software was gotten for free and it claims to be nulled, I would strongly suggest not attempting to upload it here. We have a Zero Tolerance policy to nulled/hacked software, and it always results in a permanent account suspension.
If you can confirm that your copy of vBulletin is legal and officially licensed to be used on your Free Hosting account with vBulletin, then proceed to upload the contents of the forum software to your account (into the public_html folder) and set up the database via cPanel, then install the software. If it is nulled, or not licensed, I would use software such as SMF, phpBB or MyBB, which are free pieces of software that we offer auto-installation support for. If you wish to install one of these, visit Softaculous in your cPanel account and simply install it via that program.