I’m not able to update my iPhone

What are you trying to update on the phone? What model phone is it? What happens when you try? Are you trying to do an IOS update? More information would help.

iOS 13 and iPadOS are compatible with these devices - Apple Support.    

iOS 12 is compatible with these devices.    

IOS 10 is compatible with these devices    

Update your iOS device.        

Get help with over-the-air iOS updates          

Update – Can’t or can’t restore 

If you see an error when you update or restore your iPhone, iPad, or iPod      

See if this helps. Maybe you were unable to connect to the App Store, iTunes Store, or other Apple services https://support.apple.com/en-us/HT201400.