How do I upgrade the linux cnc software

I have linux cnc as part of my ubuntu operating system. actually linux cnc was was already built in. Now my ubuntu version needs an upgrade. how can I do that without losing linux cnc?

The short answer is you can't.

Upgrading the Ubuntu version will install a new kernel, and the versions from Ubuntu will not be real time kernels and therefore not compatible with Linuxcnc.

Linuxcnc has migrated to a Debian distro for the newer live installation disk images, although even that is now eol. I expect that in the next 6 months or so there may be a new ISO image from Linuxcnc that will hopefully be based on a newer distro. (An RTAI patched Debian 9 would be very nice, but I'm not going to hold my breath waiting for it.)

If you really want to stick with Ubuntu, You will have to install the newer version of Ubuntu, Then install a realtime patched kernal for that version of Ubuntu, then either compile and install Linuxcnc for that kernel you installed, or if you were able to find and install a version of Ubuntu that is supported by buildbot, you can install using those repos. (I think Precise is the only choice and it is also eol.)

Okay great, thanks for that thorough and speedy reply. So... say I don’t give a crap about anything on the computer and I don’t care about Ubuntu . I just want to run Linux cnc for my router. How do I start fresh and upgrade the os and Linux cnc for free ?

I would download the curent ISO, burn it to a DVD or USB drive and install it from there.
www.linuxcnc.org/linuxcnc-2.7-wheezy.iso

But before you install I would highly recommend copying and backing up your config files for your current installation.

After Installing run the update program to get Linuxcnc (and everything ese) up to date. Then copy your old config folder to the linuxcnc folder in your home folder of the new installation. You should then be able to run your machine. (if you don't need to make any config adjustments from version updates.)

What version of Linuxcnc are you currently using? There were some minor changes between versions 2.5 and 2.6 that may require minor changes to your hal file to get your old config working. These are all mentioned in the installation chapter of the documentation.

that sounds good. but it doesn'tcome with an OS right? so I will need to put an OS on my computer too. latest ubuntu or whatever that's free correct?

It is a complete live system and comes with Debian 7 (Wheezy) as the OS, and XFCE as the desktop. (I'm not a big fan of XFCE and usually replace it with Mate.)