Unable to update my iPhone 7 Plus software

Software update problem

The real problem is that your iPhone 7 Plus is too old to run iOS 16, iOS 17, or iOS 18, if that is what you are trying to do.

If this is not what you are trying to do, please provide more details.

An iPhone 6/6 plus can't be updated beyond 12.5.7, it doesn't have the hardware required to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, or SE 1st generation, you can update to 15.8.3

• If you have an iPhone 8 or X, you can update to 16.7.10

• If you have an iPhone SE (2nd generation or later), or XR through 16, you can update to 17.7.3 or 18.2

That phone can’t run anything later than ios 15. 16 requires an iPhone 8 or newer. 17 and 18 require an iPhone XR or newer.

Unable to update my iPhone 6 software

That is correct. You are not able to update the iPhone 6 to anything higher than iOS 12.5.7.

updated my I phone 6 to iOS 15

No, you did not do this, because you cannot do this.

No you didn't, an iPhone 6 can run iOS 12.5.7, no further.