iPad mini kullanıyorum güncelleme gelmiyor artık kullanılmıyor ne yapabilirim

If your iPad is eligible for an update, then go to: Settings -> General -> Software 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)

You need about 7 GB device storage and good Wi-Fi.

If they are On, turn Off Hotspot & VPN.

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

I bought it new, so why can't I open it, I can't install it, its memory is empty.

See the following Apple articles:

Turn on and set up iPad

Turn on and set up iPad – Apple Support (UK)

Set up your iPhone, iPad, or iPod touch

Set up your iPhone, iPad, or iPod touch - Apple Support

I can't update YouTube doesn't open

Update the iPad has nothing to do with TouTube.

Have you buy the iPad 2nd hand?