Help me to find iOS 12.5.5 to iOS 14.0

Please check the model of iPhone that you have. If you are not sure.......

Tap Settings

Tap General

Tap About

Look for the Model Name

You will likely find that you have an iPhone 6 or an iPhone 6 Plus

If that is the case, iOS 12.5.5 is far as you can go. That is the end of the line. The iPhone 6 and 6 Plus cannot be updated any further than iOS 12.5.5.

If you really do need a higher operating system, you will need a newer phone.

You have not mentioned which model phone you are trying to update. If it is an older model, it is probably incapable of being upgraded beyond iOS 12.5.5.

If you are running iOS 12.5.5 now, then your iPhone is not compatible with anything later than iOS 12.