I can't update my Mac OS X?

I'm trying to download Minecraft after a while of playing it and it says that I need to update my iMac to the latest version, I'm currently on version 10.7.5 and I need to be on 10.8 or later but when I try to update my software it says that there's no updates available, what do I do?

Brooklyn 15.08.2018

If the machine is not capable of running the very latest version (which should be free in the apple store), you have to buy the appropriate upgrade.