There is a caveat here though, and that is the device must be running system software later than version i OS 5.0, so older hardware may be left out.
In any case, if you are running i OS 5 or later, you can use OTA to update i OS with no attachment to a computer or PC whatsoever.
If the interface seems more sluggish, apps take longer to open or run and it just isn't the swift device you remember, a few tweaks could speed things up.
All computing devices are prone to slowing down over time, as their memory fills up and extra software is installed, but the way i Phones use their memory makes them less prone to this than most.
Instead, upgrade paths for both devices will end with i OS 5.
The i Phone 3GS and its 256MB of RAM, on the other hand, will be receiving i OS 6.
This is a safety measure that will ensure you do not lose any contacts, messages, pictures, or other important device data.
You may also find that your phone is a bit slow if you haven't got a lot of space free, even if it's a newer model.
Or maybe your i Phone has been performing more slowly since you installed the latest version of i OS.
It's possible that it just slower than it used to, because you've got used to what initially seemed dazzlingly quick operation, or have started to compare it to friends' newer, faster models.
But sometimes it's possible to make a direct comparison: when there's an app you used to enjoy but has since become unusably juddery.