How do I change my Apple ID on my iMac?

How to change user account name or home directory name:

http://support.apple.com/kb/HT1428

https://discussions.apple.com/docs/DOC-3872

System Preferences-Users and Groups- Change ID

I tried this, but although it changes Apple ID on Users & Groups screen, when I try to update apps in the App Store it still uses the old Apple ID?

I have the same problem...