Hi sir I want to update iOS 15

shanif17 Said:

"Hi sir I want to update iOS 15"

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To Check for Updates:

Use a Computer and Ethernet:

Start with attempting an update through use of a computer. If you cannot use Wi-Fi, then use Ethernet.  Go Here: Update your iPhone Using a Computer - User Tip. On the computer, you would connect it through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple

have you read

Update iOS on iPhone - Apple Support