When you restore to an iCloud backup you should be given the option to restore to previous backups (up to three) if they are available. This is mentioned under "iCloud - How to restore from a backup" here: http://support.apple.com/kb/HT1766.
If you need to restore an iCloud backup on a device that has already been set up, you have to erase it, then go back through the initial setup screens to select to do so. If you have any data on your device now that is not in the backup that you want to save you'll need to do that first. Then go to Settings>General>Reset and tap Erase All Content and Settings. You will then go through the setup screens as you did when the phone was new. When given the option, choose Restore from iCloud Backup (see image below). Be sure you are connected to wifi and your charger as this will take some time to finish.