I am currently running Photoshop CS5 on my pc. Once I join Creative Cloud will I have to remove CS5 before downloading CS6?
No need to remove. They can co-exist. The two that cannot co-exist are Photoshop CS6 Beta and Photoshop CS6. So if you participated tried the beta you would need to remove that.
Do you have to remove the beta before you can install CS6 Photoshop or will the installer see that it is there and uninstall it? What is the best way to uninstall it, if it does not happen automatically?
Installer will not uinstall the Beta , you have to uninstall it by yourself before installing the CS6 and to remove Beta is highly recommended.