I want to Update my iPhone

Please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

Go to Settings-> General-> Software Update. Wait until you will see the version available. Then click Install button. After that enter your IPhone's password. Then read the License Agreement and click Agree button. Wait until your IPhone is updating.