How to get iOS 6 if it my device hasn't been updated since iOS 4?

I've obviously missed a few updates and want to update it to the newest iOS but I don't know how, help?

Added (1). I have an iPhone 3Gs

Your device is probably too old to update to ios 6, but try under settings and system update.

What iOS device do you have? Since you're still on iOS 4, chances are that your device is too old and obsolete at this point.

These are the devices that support iOS 6:
iPhone 3GS
iPhone 4
iPhone 4S
iPhone 5
iPod Touch (4th generation)
iPod Touch (5th generation)
iPad 2
iPad (3rd generation)
iPad (4th generation)
iPad Mini (1st generation)

If your iDevice isn't on here, then it isn't supported and can't be updated to that version.

It depends what your device is. It is is 3gs, ipod 4, or ipad 2 or above, it can be updated. Besides that, you can't get iOS 6. Besides, i think you would have to get iOS 9 if you have 4s, ipad 2, and ipod 5 or above.