My Macbook air 2012 running 10.8.5 can't seem to install 10.9.0

So i just got a bunch of old computers from my father in law including a macbook 5.2 and a macbook air mid 2012.

I'm not a apple user and i have no idea what i'm doing but i'm quite tech savy but still i can't figure this out.

so i cleaned the whole computer and reinstalled it. it installed mac osx 10.8.5 i want it on catalina but for that i need 10.9 or higher but i can't seem to install 10.9 anywhere on the app store and on the support website i couldn't find anything either. only updates for 10.9 but that doesn't help me.

I read somewhere i need to buy a installation disk.. so i downloaded one. All seemed good but when i select my hard drive and press install nothing happens.

anyone has a idea how i can update this thing to a higher osx?