Changing accounts in app store iPhone

Hello everyone! I have two app store accounts, 1 is HK and 1 is Japan and I have some apps downloaded from these two app store.
I have some apps downloaded from Japan app store needed to update but I cant updating them. After logout out the HK app store account and login the Japan account successfully, but there pop up an password request box and it show my HK app store account. Even I reset all my iphone setting, it still cannot be able to update the apps, it still requesting my HK app store account password.
But I can download apps from Japan app store after I login.
Could anyone give me a suggestion for helping me to solving this problem?
Many thanks!
iphone 3Gs iOS 4