Why my iPhone cannot connected wifi

You need about 6 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

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

ravinitha Said:

"Why my iPhone cannot connected wifi: Why I cannot update software"

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What's the model of your iPhone?

Updating an iPhone:

A. Computer:

Do so using WiFi or Ethernet on a computer.

Use my User Tip:  Update your iPhone Using a Computer - User Tip

B. Cellular:

Updating your iPhone using Cellular might be an option, depending on your iPhone model. If not, it would be because the model simply does not have the builtin hardware for this. See my User Tip: Use an iPhone 12 or later, that is using 5G, in order to update over Cellular - User Tip

Back Up First:

IMPORTANT: If you have an option to update, however, then be certain you backup your iPhone first. That way, you will have something to restore your iPhone from should anything go wrong with the update.