Can i update my iphone 3g to the current ios?

When i try to update it thru itunes, a pop up would appear and it said that ios 4.2.1 is up to date and is the current version.

do you have any idea how to update it to ios 5 or 6?

Added (1). Well that sucks because most of the apps i'm trying to download in the app store says that it currently needs ios 4.3.so most of the apps i want can't be downloaded.

You can't. Only the 3gs and up are able to update past 4.2.1.

No, iOS firmware 4.2.1 is the highest available firmware for the iPhone 3g. What that means is that from iOS version 4.2.2 to the current version, the iPhone 3g is not supported. The likely reasons for this is that the new features would cause the phone to run slowly, cause glitches or bugs, or drain the battery at an incredible rate. If you need more information send me a message on my youtube channel: TheWeeklyRepository.

That's because 4.2.1 is the current & last version available for the iPhone 3G. To get to iOS 6 you would need to get an iPhone 3GS at least.