I could not update my I phone

We need details in order to help you. Do you see an error message? What makes you think it isn't updating?

Click on this link to read how to "Update your iPhone, iPad, or iPod touch" --> https://support.apple.com/HT204204 - When you try to update you will only be given one update selection which will be the highest available iOS version supported by your device. If it says no update is available and you need a higher version you will have to buy newer equipment.