When you connect to your Web Hosting account with your FTP tool, you'll see a display of the folders and files in your web site. Generally this display will look a lot like the files and folders on your computer — and you can move them around, delete them, and rename them the same way you'd work with files on your own computer!
To move a file, you can generally click on the file once and, holding down your mouse, drag the file to its new location. To rename the file, try clicking the file name with the right button of your mouse, then selecting the "Rename" option.
For detailed instructions, please see your tool's documentation.
NOTE: As of February 19, 2013, Yahoo! Small Business has completed the transition from supporting FTP to FTPS. To avoid any connection issues, please make sure you have updated your FTP client to use your FTPS settings.