What you do is you go and plug up ur iPhone to the iTunes and click on the update button
Yes the iphone 4 is better so you should upgrade to the iphone 4.
iOS 4 was released long ago back in 2010 along with the iPhone 4 and was a free update. It could be downloaded on any device except the original iPhone and 1st generation iPod Touch.
Simply update ios
it will not update and if it does it might lock your phone and you will not be able to use it.
depends if it has 4.os update
Yes, if you update it to iOS 5.1.1, there is an untethered jailbreak out.
plug your iphone into your computer and go into itunes click on your phone under devices go to summary and press check for update or update iphone.
No.
Update the software in iTunes and it will do it for you.
yes. the current update is 3.1.3 and to update to it you have to restore you iphone, update it then re-jailbreak it. but at this moment in time this is not an jailbreak for firmware 3.1.3.
The update 6.1.6 helps to maintain the working efficiency for the iphone 3gs.
I don't believe the iPhone 3G can update past 4.2.1, but any newer iPhone can update the same way you normally update an iPhone through your iTunes authorized computer.