I have recently upgraded my 12.04 LTS Ubuntu to 12.10 Ubuntu. During the installation process Third Party Resources were disabled. The dialogue suggested that "Some third party resources in your software.list were disabled.You can re-enable them after the upgrade with the 'software-properties' tool or your package manager.
Please guide how to enable third party sources? I don't find any interface were I can control enabling or disabling of third party sources.
Please note that I have Ubuntu Software Center and Update Manager installed.
Please also note that I had Redshift installed on my computer since 12.04 but the same is not working in 12.10.