How to download ios14.0

This is not possible, since iOS 14 is no longer available.

If you have an iPhone 7, you can update to iOS 15.7.5

If you have an iPhone 8 or higher, you can update to iOS 16.5

Update your iPhone or iPadAppleOfficial Apple Support › en-us

iOS 14 is not available for any phone. See here on how to update to the current version for your phone. Update your iPhone or iPad - Apple Support