On my device I don’t have software update opection

Within the Related Article above, the option may not exist among apparent items shown.

(Since those all point to iOS 15.x 'parts', probably not useful. Try the main support article

links supplied below, though details may vary.

Update your iPhone or iPad - Apple Support

//support.apple.com/en-us/HT204204

An iPhone7 model fully update to iOS15.7.8 directly from its own Software Update in Settings.

Can your iPhone get an update through use of Software update in its iOS Settings?

..If not by Wi-Fi, you may need to attach the iPhone to a Computer by USB cable..

One of those: with small 'Lightning' connector, on one end; and USB-A on other?

Update using your computer

1. Connect iPhone and your computer with a cable.
2. Do one of the following:

• In the Finder sidebar on your Mac: Select your iPhone, then click General at the top of the window.
  • To use the Finder to update your iPhone, macOS 10.15 or later is required. [With earlier versions of macOS] ~ use iTunes to update your iPhone.
  • In the iTunes app on your Windows PC: Click the iPhone button near the top left of the iTunes window, then click Summary.

3.Click Check for Update.

4.To install an available update, click Update.

IF nothing else works: You may need to try "iOS Recovery" mode.

Instructions here vary considerably from regular install paths.

If you can't update or restore your iPhone or iPod touch - Apple Support