How to update to an earlier iOS version?

You have an iPhone 6s Plus and it can be updated to iOS version 15.7. The WhatsApp app will not work on your currently installed iOS version 11.4.1.

You can install iOS version 15.7, however you do not have enough free storage space available on your iPhone to complete the update. You will have delete data on your iPhone to create the necessary free space of at least 6GB. Media files take up the most space so begin by deleting Videos, Photos, Music and apps that you don’t use. Once you have created about 6GB of free space on your iPhone, then you can try and update your iPhone again.

Axel F.

1.

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

2.

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

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

See this Apple article: Upgrade to iCloud+ -< Upgrade to iCloud+ - Apple Support

See also: iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support

Manage your iCloud storage

Manage your iCloud storage - Apple Support

3.

Check iPhone model & iOS version -> Go to: Settings -> General -> About.

If it is an iPhone 6 (and other older iPhone type) is an outdated iPhone it can’t be update to a higher iOS (13 and later).

The last security updates iOS 12.5.7 -> available for iPhone 6.

If it is iPhone 6S Plus you can update to iOS 15.7 

Go to Settings -> General -> Software Update -> Download and Install.

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