Your current version is 10.11.6. There is no "in between upgrade" to get to 10.12. Unfortunately, you have not provided the full information on your MBA model. To find the complete model information select About This Mac from the Apple menu. We need this information in order to find out what the highest version of macOS is supported by your model. You can create a snapshot of the dialog as follows:
How to take a screenshot on your Mac
Capture, Save or Record Screenshots in Mac OS X - Help Desk Geek
OS X Screen Capture Shortcuts
(⌘⬆︎3) Command-Shift-3 Capture the screen to a file
(⌘⬆︎⌃3) Command-Shift-Control-3 Capture the screen to the Clipboard
(⌘⬆︎4) Command-Shift-4 Capture a selection to a file
(⌘⬆︎⌃4) Command-Shift-Control-4 Capture a selection to the Clipboard
(⌘⬆︎5) Command-Shift-5 Invoke new screen grabber
You can then post the image in the forum's message editor.