I need to update my phone to iOS 14.0

iOS 14 is no longer available. The currect iOS version for an iPhone 7 is 15.7.5

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, you can update to 15.7.5

• If you have an iPhone 8 or higher, you can update to 16.4.1(a)

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support