Update my iPhone 6 to iOS 13.4

An iPhone 6/6 plus can't be updated beyond 12.5.7, it doesn't have the hardware needed to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

To update to 12.5.7 -

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 Update your iPhone or iPad - Apple Support

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

Update iOS on iPhone - Apple Support

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support

rk0483 Said:

"Update my iPhone 6 to iOS 13.4: iOS 13.4update immediately please update in 7 days"

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Updating an iPhone 6 to iOS 13.4:

A. You can't.  The iPhone 6 will only install to iOS 12. See here: Update your iPhone or iPad Software if you're Experiencing Issues with Location, Date, and Time - Apple Support. And, for the note, even if you could update, only the latest compatible version will install.

So, what to Try:

B. Update Using a Computer:

Have a Computer Handy? If so, try using a computer to update. Go here: Update your iPhone Using a Computer - User Tip. If any updates are availabe, they will install, sure enough.