I need to upgrade iOS

Assuming you have a compatible device, 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. 

To update your iPhone, select Settings > General > Software Update. If your phone is eligible for an update, you will be prompted to do so. You can read more about it here:

Update your iPhone or iPad - Apple Support