Why does my phone no wanna update ??

What happens when you go to Settings -> General -> Software Update?

If your iPad is eligible for an update, you can check by reading this Apple article:

iPad models compatible with iPadOS 13 to iOS 15.2

iPad models compatible with iPadOS 15.4 – Apple Support (UK)

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

If they are On, turn Off Hotspot & VPN.

Correction:

If your iPhone is eligible for an update, you can check by reading this Apple article:

iPhone models compatible with iOS 15

iPhone models compatible with iOS 15.4 – Apple Support (UK)