Update Your Device
If you want to avoid a huge download when iOS 11.3 arrives, make sure your iPhone, iPad or iPod touch is running the latest software.
It's extremely easy to fall behind now that Apple releases a new iOS update every few weeks.
If you aren't sure what version of iOS you're on, go into your device's Settings and tap on About. Look down to where it says Version.
If you aren't running iOS 11.2.6, consider downloading the latest version of iOS 11. This way, you'll avoid an enormous download and your device will be stocked with the latest bug fixes and security patches.
Be sure to read reviews before you make your move.