I need to update my iPhone 6s to iOS 13.4

iOS 16 is only compatible with the following devices. Unfortunately, you cannot update your iPhone 6s to iOS 16.

• iPhone 14 
• iPhone 14 Plus 
• iPhone 14 Pro 
• iPhone 14 Pro Max 
• iPhone 13 
• iPhone 13 mini 
• iPhone 13 Pro 
• iPhone 13 Pro Max 
• iPhone 12 
• iPhone 12 mini 
• iPhone 12 Pro 
• iPhone 12 Pro Max 
• iPhone 11 
• iPhone 11 Pro 
• iPhone 11 Pro Max 
• iPhone XS 
• iPhone XS Max 
• iPhone XR 
• iPhone X 
• iPhone 8 
• iPhone 8 Plus 
• iPhone SE (2nd generation or later)

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

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

If the above Apple articles do not help, please post back with relevant information. 

The iPhone 6S can be updated to iOS 15.7.

The iPhone 6 can be updated to iOS 12.5.6.

ridwan60 wrote:

I need iOS latest update for iPhone 6s

The most recent iOS version for iPhone 6s is iOS 15.7.

You’d probably already be running that or something close, but this iPhone is probably short on available free storage, which means the update to iOS 15.7 will require using Windows or Mac. That update path is included in the following article:

… Update your iPhone or iPad - Apple Support

As mentioned in replies above, iPhone 6s cannot be updated to the just-released iOS 16, but the also-just-released 15.7 will get you working for your iOS 13.4 or newer requirement.