Software & OS Versions for (Very) Old Mac

Hi All

I was given an old (2010) iMac a little while ago and I was wondering how I can check what the absolute latest versions of the OS and pre installed software it can run are?

The machine is running bootcamp and the Mac OS was never actually used during its 'working life', I've already run the software updater and it's now telling me everything is up to date (the OS is Mac OSX Version 10.6.8) and I don't seem to be able to update either the OS or apps like Safari and Garage Band any further even though I'm being prompted that there are updates available when I load the apps. Obviously I know there are limitations in support because of the age of the hardware but is there a way to 'force update' the OS and at least some of the software to the latest or more recent versions than I currently have access to?

Thanks