The README-UPGRADE.txt that comes in the installation packet should be sufficient to show you which files to back up and exactly how to install the component and modules. Did you follow this carefully the first time you tried the install? Have you utilized any hacks or user level access control extensions? Why do you think your site is now "botched"? See my signature for more information to include.
The Documentation Subscription gives you even more information to make the most of CB 1.2.