Unable to update iOS on my iPhone 7

Care to provide more details re. the failure? How are you attempting the update: Over The Air, or using a computer? How much free space is available on the device? What is the error message?

Note that the max. version your iPhone 7 can use is iOS 15.7.4.

Hello ~ In addition to * Courcoul’s* information take a look here by clicking on below…

If your iPhone or iPad won't update - Apple Support

~Katana-San~