Update your iPhone, iPad, or iPod touch.

New Release iOS 15.4 Download IPSW with direct links,

How to Update your device wirelessly
Plug your device into power and connect to the Internet with Wi-Fi.
Tap Settings > General > Software Update.

Tap Download and Install.
To update now, tap Install.
If asked, enter your passcode.

Update automatically
With iOS 15.4, you can have your iOS device update automatically. To turn on automatic updates, go to Settings > General > Software Update > Automatic Updates. Your iOS device will automatically update to the latest version of iOS. Some updates might need to be installed manually.

Update your device using iTunes
If you can’t update wirelessly on your iOS device, you can update manually using iTunes on a computer that you trust. If your computer is using Personal Hotspot on the iOS device that you’re updating, connect your computer to a different Wi-Fi or Ethernet network before you update.

Install the latest version of iTunes on your computer.
Connect your device to your computer.
Open iTunes and select your device.
Click Summary, then click Check for Update.
Click Download and Update.
If asked, enter your passcode.

iOS 15.4 IPSW Direct Download Links:

iPadOS 15.4 IPSW Direct Download Links: