How do I update iPhone X from iOS 16 to 17 or 18?

The iPhone X can not go to iOS 17 or iOS 18 the last iOS that the iPhone X can support is iOS 16 the iPhone Xs and Xs Max and Xr can go up to ios 17 and ios 18 those are the only x model iphones that is still supported in 2025

You do not update an iPhone X to iOS 17 or 18, because you can't.

For the iPhone X, a phone that ran iOS 11.0.1 when Apple released it in November 2017, iOS 16 is the end of the line.

The highest an iPhone X can go is 16.7.10