I need to update my phone

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 see if your phone is eligible for an update.......make sure that you have a good Wi-Fi connection and the battery is fully charged.

Tap Settings > General > Software Update

If a new update is available, it will appea so you can tap to proceed