vBulletin is a commercial forum package (bulletin board system).
Start with unzipping your product .zip/.rar file and your forum skin .zip/.rar file.
Open your FTP manager, and in your forum root, go into the folder "images" and upload your style image folder there.
Step 1: Login to your forum AdminCP -> Styles & Templates -> Download/Upload Styles.
Browse for the "something.xml" and select it. Then, fill out a style name, and the rest of the information, and import it.
Step 2: Go into AdminCP ->Styles and Templates -> Download / Upload Styles
Step 3: Under "Import Style XML file" upload your new style .xml file.
Step 4: Upload your blog.xml and cms.xml file and make sure you have your new style selected in the "Merge Into Style" droplist.
Enjoy your new style!