I have googled and found out Updates don't install because of "untrusted packages".
It didn't fixed the error. So, how do I fix my GUI update?
sudo apt-get update && sudo apt-get upgrade < working The following packages will be upgraded: ambiance-colors radiance-colors 2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 5,029 kB of archives. After this operation, 7,614 kB of additional disk space will be used. Do you want to continue [Y/n]? y WARNING: The following packages cannot be authenticated! ambiance-colors radiance-colors Install these packages without verification [y/N]?
Working but when I update from GUI or try to install software from Ubuntu Software Center I got same error as shown in above picture.
For every software I have to install it from command line because I got same error when install software from Ubuntu Software Center.