How to update my ios16.6 iphone to 18?

No. At this point, you can stay on 16.6 or update to to 26.

When i tried to update it through itunes from computer it shows me only that i can update to ios 26.

That's correct.

IF......your iPhone 12 was currently running iOS 18, you would have had an option to update to iOS 18.7. But that option would only appear if your phone was already running iOS 18.

Your only options at this point would be to update to iOS 26, or do nothing and stay on iOS 16.6.

Tip.....it's always better to update using a PC or Mac if possible.....my opinion.

Austute wrote:

So there is no other way to update to 18ios?

And if you do go elsewhere and an article says you can choose your ios version and mentions IPSW, ignore it, it's a jailbreak and leaves your security so wide open your bank apps will refuse to install.

FYI, my iPhone is currently running iOS 17.7.

When I use Software Update on the iPhone itself, I get a choice between iOS 18.7 and iOS 26. Usually the phone leads with iOS 18.7 with a line at the bottom of the screen telling me that iOS 26 is also available. But not always; sometimes it leads with iOS 26, showing the iOS 18.7 choice only after I press "Back".

I plugged the iPhone into my. Mac to see if computer-based updates behave any differently. They do. At first the Mac told me that my iPhone was up to date. After I asked the Mac to check for an update, it said that iOS 26 was available and offered to install it. There was no mention of iOS 18.7 and no choice to install it. I cancelled out and checked the over-the-air options on the phone again, and found that it was still offering both versions.

So it looks like you only get a choice if you can upgrade over the air. No telling how long that choice will last – if I remember correctly, there were only a few weeks last year during which you could choose between iOS 17 and 18 before the iOS 17 option went away.