Unable to update Macbook Air (2012) OS X 10.7.5.

When you run Applications -> App Store, and click on "macOS Sierra" on the right side under "Quick Links" what errors do you get?

I just upgraded a 2010 Macbook Air to Sierra, so I know it is possible.

Do you have enough free storage to install Sierra? That is about the only thing I can think of that would stop the install of Sierra.

<MacOS Sierra - Technical Specifications>

A 2012 Macbook Air can run Sierra.

<MacOS Sierra - Technical Specifications>

MacBook Air (Late 2010 or newer)

Notice the "or newer".

As I said, I just upgraded a Macbook Air older than yours to Sierra. There should be no problems upgrading yours.

I would try doing the upgrade from Safe mode

Try booting into Safe mode

<http://support.apple.com/kb/ht1564>

This will not load any 3rd party additions, it will load some more conservative Apple drivers (may cause screen flicker), and it will clear some kernel caches (a cache is saved data in a form that can speed up a program, but is totally redundant to the original source, and thus can be safely cleared). Booting into Safe mode is just an experiment, but can often times eliminate any 3rd party interference, or a cached item out-of-sync with the world.

Because you are on Lion 10.7.5 you have multiple steps to get to the latest macOS release.

You first need to upgrade to El Capitan 10.11. Then you can upgrade to High Sierra 10.13

This is because the minimum system requirements for High Sierra require a starting point of Mountain Lion 10.8 or higher. And there is NO reason to make you pay for Mountain Lion, when you can get El Capitan for free.

Upgrade to OS X El Capitan

<https://support.apple.com/en-us/HT206886>

Launches the App Store pointing at the El Capitan download, assuming Snow Leopard has the first 2 updates have been applied to Snow Leopard

<https://itunes.apple.com/app/os-x-el-capitan/id1147835434?mt=12>

Once you have El Capitan, you can use Applications -> App Store to upgrade to High Sierra 10.13.2

Please help me im having the same issues and since you have the 2010 i would super appreciate it. I have a 2012 and Its not allowing me to update and im at 10.7.5. Im not very computer savy when it comes to things and i wasnt even aware how old mine was running because when i check software update it says im up to date. But after using my friends whos up to date as of now I noticed the difference. I really dont want to buy a new computer so any and all advice is much appreciated. Thanks

Michi

I was having the same problem running a MacBook Pro (late-2012). I was trying to update to High Sierra from Mountain Lion following a system restore.
The main issue appeared to being Unable to sign in to Apple ID when trying to upgrade to High Sierra. Although I received the verification code in another device I could not type it in Mountain Lion.
I tried the method of installing El Captain first and got the message "not supported".
What worked for me was to use a different (non-icloud) Apple ID.
I actually created a new Apple ID, but when asked to verify the email from apple I also had to do it from another device since the OS Mountain Lion would not allow open the new account verification email. Once I managed to sign in with the new non-icloud Apple ID I was able to upgrade from Mountain Lion straight to High Sierra.
Hope this helps.

Thank you BobHarris

This was very helpful