How do I update my iPhone to iOS 16?

You do not update your iPhone 6 to iOS 16, because you can't.

The iPhone 6 cannot update past iOS 12. It has only 1 GB of RAM. All iPhones that can run anything higher than iOS 12 have at least 2 GB of RAM. The iPhone 6 also completely lacks a Neural Engine co-processor like the ones which all iPhones that can run iOS 16 and higher have.

Probably you are looking for iOS 16 becuase --> Apps that require higher iOS versions than your device can be updated to... - Apple Community

iPhone 6 is supported with iOS 12, and no later.

You’ll need a newer or new iPhone.

Donsasco: If no updates are offered, then you’re either still enrolled into an old beta, or there are no newer versions compatible with the particular iPhone.

For access to iOS 16, an iPhone 8 or iPhone X is required. iPhone XS, iPhone XR, and iPhone SE 2nd gen, and newer, can get to the current iOS 18.

MrHoffman wrote:

For access to iOS 16, an iPhone 8 or iPhone X is required. iPhone XS, iPhone XR, and iPhone SE 2nd gen, and newer, can get to the current iOS 18.

For the iPhone XS and XR, iOS 18 is the final major update. They won't receive iOS 26 when it comes out in the fall.

Apple Intelligence requires an iPhone 15 Pro, 15 Pro Max, or 16-series phone. I'm guessing that there will be 17-series phones this fall and that they will support Apple Intelligence, too.

I want to update my phone but they didn’t give me updates

The updates are available, but your phone is not qualified to receive them.

To receive iOS 16, you need an iPhone 8, iPhone 8 Plus or iPhone X.