Just as the question says, I need to install newer version of Ubuntu without messing up the older version. I have looked at the responses to similar questions but it isn't clear to me how to do so (some suggest dual boot using a second hdd and some suggest using virtualization -- both of these are not an option for me).
You should get the option to install alongside, it will not try to use a second drive if one is not available, it will attempt to create a logical partition within the existing setup.
You back up your existing install and the either shrink existing partitions and use the Something Else option to manually set partitions or let the installer do so.
If you do that the NEW install will install grub and the OLD system will be available as boot entry.