You have 2 options
1. Buy a new iphone.
2. Tap Settings > General > Software
Update. Tap Download and Install. Updates
might download automatically while
your device is connected to Wi-Fi and
a power source.
Tap Install, or tap Later to install the
update later. If you use a passcode,
you'll need to enter it before installing
the update. You need to also buy a lot of data. Update could be up to 1GB or more.