How can I update my iOS to 15.5

To update to the most recent, compatible version of iOS, please 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. 

If you're referring to an iPhone 6s, iPhone 7, or iPhone SE 1, use a computer or the Software Update function in Settings. Other models aren't capable of 13 or above, or can only be updated directly to 16.6.

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You cannot update to iOS 15.5. However, if your iPhone is qualified, you can update to iOS 15.7.8.

Do you have an iPhone 6s or iPhone 7? If yes, see this Apple Support document on how to update.

Update your iPhone or iPadApple SupportOfficial Apple Support › en-us

If you have an iPhone 8 or higher model, you can update to iOS 16.6

iPhone 6 Plus can update to iOS 12.5.7. No more updates are available for the iPhone 6 Plus

If you want to run iOS 15, you need an iPhone 7

If you want to run iOS 16, you need an iPhone 8

If you want to run iOS 17, you need an iPhone XR, XS or higher model

no is not updated

I have iPhone 6plus

How

5prince wrote:

I have iPhone 6plus

That model can be updated to 12.5.7, no further.