I’m unable to install iOS 15.4.1 on my iPhone 7

and memory left also about 3gb

Try to free up iPhone device storage see this Apple articles below:

If you need more space for an update on your iPhone, iPad, or iPod touch

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

How to check the storage on your iPhone, iPad and iPod touch

How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)

Clear Other storage on your iPhone or iPad

Clear Other storage on your iPhone or iPad - Apple Support

-> What's the difference between device storage and iCloud storage?

What's the difference between device storage and iCloud storage? - Apple Support

Raicya Said:

"I’m unable to install ios15.4.1 on my iPhone 7 after downloading it’s downloaded and memory left also about 3gb"

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Try Removing Of Data from the iPhone itself...

Troubleshooting iPhone Storage:

Internal storage cannot be upgraded. It is what it is. So, the maximum internal storage capacity never increases, even if you upgraded your iCloud plan. Learn More here: What's the Difference Between Device Storage and iCloud Storage? Apple Support. 

So, what to do:

Clear Space:

Try clearing internal storage though use of the following:

What Space to Clear:

A. Clear Temporary Internet Files:

Clear your Temporary Internet Files(Cookies & Cache) of Safari:

• Cookies perform remembrance of certain site-entered data.
• Cache keeps a snapshot of the last time you visited a site.
• Go Here: Clear the History and Cookies from Safari on your iPhone, iPad, or iPod Touch - Apple Support

And...



B. Clean TV and Music Libraries:

Remove all unneeded files from your TV and Music Libraries. Full-Movies take up 2-4GB typically, and a bunch of those would take up a load of storage, ideally. So, if you have any movies that are not needed, then delete them.

And...

C. "Other" being the Culprit:

Use this Link: How to Check the Storage on your iPhone, iPad, and iPod touch - Apple Support. The storage named "Other" is the grey bar. So, to clear that, this is what to perform: Clear Other storage on your iPhone or iPad - Apple Support

Try first to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

If you still don't have a 'service' after that, see -> iPhone 7 Repair Program for "No Service" Issues

iPhone 7 Repair Program for "No Service" Issues - Apple Support

Go to: Settings -> General -> Software Update.

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

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

If they are On, turn Off Hotspot & VPN.

kaunhaitu Said:

"I’m unable to install iOS 15.4.1 on my iPhone 7"

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Updating your iPhone:

Update Using a Computer:

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

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.