Bought a second iMac a few days ago..

My "newer" iMac is a mid 2011 2.5 ghz model whereas the old one is 2008 2.8 ghz running Maverick.
I had backed up my old iMac on an external drive using Super Duper.
Using Migration Assistant, I transferred files to my new Mac.
Then tried to do the updates (I can't recall what OS the new Mac was running) but the previous owners Apple ID was still in the system so going on-line I read that I needed to do a clean install. Followed procedures.
Got Internet Recovery,Disk Utility, erased hard drive, Partition, then the Install OSX option. The only choice there was OSX Lion. I thought Yosemite would be available, or at least Maverick, so I clicked on Lion and that's what I have now.
I did another migration assistant and my iMac looks to be ok, no issues yet except a few programs in the Applications folder that have slanted bars across for some reason.
Anyhow, I've downloaded Yosemite but not installed it, still need to read up on the pros and cons and procedures.
Now, here's my question: how do I install Maverick? I had it on my older Mac because I upgraded from Snow Leopard. If I decide to stay with Lion for a while, what features do I lose out by not having Maverick?
I wonder why it wasn't on the choices I could make when in Internet recovery Mode?
I would have thought that doing the Migration Assistant would have not only brought all the files but also upgraded from Lion to Maverick. Guess it's something I would need to do in disk recovery mode?

Migration Assistant doesn't touch the OS files, just your files. The slanted bars probably mean that the version of the software won't run on Lion, so it's not available to you.

To install Mavericks, assuming you have an Apple ID and used it to install Mavericks previously. Login to the Mac App Store and then your purchases and search for mavericks. The installer should be there. Download it, cancel it when it starts to run, or you can let it run and update what you have. Your choice. It probably wasn't on the options for you on Internet Recovery because it was recovering what you had.

Disk Recovery Mode may be a better solution, but I don't think they had introduced that in Lion, so you may not have a recovery partition. No harm trying.

Thanks. Learnt something new.
Much appreciated.