If you can update to iOS 16.4.1 (a), you can check by reading this Apple article: iPhone models compatible with iOS iOS 16 -> iPhone models compatible with iOS 16 – Apple Support (UK)
Go to Settings -> General -> Software Update -> Download and Install.
You need about 6 GB device storage and good Service and/or Wi-Fi.
If they are On, turn Off Hotspot & VPN.
Charge the battery > 70%.
See the following Apple articles:
Update your iPhone, iPad, or iPod touch
Update your iPhone, iPad, or iPod touch - Apple Support (IN)
If your iPhone, iPad or iPod touch won’t update
If your iPhone, iPad, or iPod touch won't update - Apple Support
You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC
Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)
If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder
Update your iPhone, iPad, or iPod touch with the Finder - Apple Support