Snow Leopard to El Capitan – would really like to find a way to get Garageband

I have an older iMac w/ Intel Core 2 Duo 1.83 and 2GB RAM.  From what I read I should be able to upgrade to El Capitan, but it says I can’t.  I have all the software updates installed and the OS X version says 10.6.8    I’m new to Apple, and would really like to get Garageband, and thought if I upgraded to El Capitan, I could get the newest version which is probably much better than the older one.

So, maybe I’m stuck with Snow Leopard and need to figure out how to get Garageband on it?

Or, why can’t I upgrade to El Capitan ( the iMac seems to meet all the system requirements – at least 10.6.8, 2GB RAM, and Intel Core 2 Duo 64bit CPU) so I can get the new version of Garageband?

Thanks in advance.