Why is my ipod not upgrade to 4.2.1 ? serial number , 9C911QWG208

2nd gen can go to 4.2.1

Identifying iPod models

Which do you have. Read the articel above and check

As I read the question the OP was asking how to upgrade to iOS 4.2.1 on the iPod 2nd gen.

This would be done using iTunes on your computer. If you are having problems doing this you will have to give more information as to what the trouble is, error messages, etc.

Expand the section titled: Update your device using iTunes in the document here for update directions: http://support.apple.com/kb/HT4623

To see Devices which is referenced in the document use Show Sidebar from the iTunes View menu.