Hi - fully accepting in advance that the problem is likely to be with my skills and not the machine or programs - here's my issue. And, yes, I have checked other posts but frankly have gotten a little lost in many of the details.

I have tried in several ways (typically following the Ubuntu documentation) to upgrade my distro as numerous functions are not working and are now unsupported. All have failed to achieve the result I anticipated. I'm stuck in an older version and that seems to be that. I have a screenshot of my last command line efforts (sudo apt-get [insert several variants from the Ubuntu documentation]that all finish with "an upgrade from 'vivid' to 'xenial' is not supported with this tool"

The process has worked previously, my assumption is that having let the laptop/software lay idle I may be too many distros apart between the existing version and the latest one (?)

I'm also keen to know if I can just boot onto the newest version with the CD drive (the way I originally installed Ubuntu.

Anyone disposed to offer some practical guidance will e enormously appreciated :-)

Personally, I would just start again with a clean install, of the latest version of your distro, of choice, if possible. As that would be the easiest option from your question.

Good luck!

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Welcome to LQ!

I am not a 'Buntu user so have no specific help to offer for your problem.

But I would suggest that you will get better answers if you supply a little more information, such as your current version, the methods you have tried to update and how they failed with some specificity and an overview of your hardware. The more info you provide the better others can help you.

And I tend to agree with the previous reply, all else being equal I usually prefer to backup my personal data and start fresh rather that follow an unfamiliar or problematic upgrade path.

Good luck!

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The most likely reason you can't upgrade your "older" version of Ubuntu is because it is not supported any longer. Since you don't indicate which release you are using, you can take a look at the Ubuntu site below and find whichever release you are using which will probably be in the
"End of Life" section.

https://wiki.ubuntu.com/Releases

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and that is that.
[ you could try aptitude, but i'm not sure if it's even supported for ubuntu (which is NOT debian). anyhow, not recommended. ]

more likely:
https://wiki.ubuntu.com/Releases
note how vivid vervet is under the EOL section.

save your personal data and reinstall.

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Vivid (15.04) was a non-LTS release, so you have to upgrade to the next non-LTS release (Wily 15.10) before upgrading to Xenial.

Remember to back up all your data before upgrading in case things go awry.

It's generally advisable to stick to LTS releases unless you have an abiding reason not to.

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Upgrading to a release that is no longer supported doesn't work the same way as a still supported version as the repositories are moved when support ends. It is possible in Ubuntu but not really a simple process for a new user. Explained at the Ubuntu site below. Who knows how old the system the OP is using is?

https://help.ubuntu.com/community/EOLUpgrades

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If you have lots of software suffering from bit-rot due to doing upgrades every 6 months, including missed upgrades.
When when I used Ubuntu a few years back, I came to the conclusion that it was best to ignore the trial software released every 6 months.

Provided you don't have massive amounts of user customisation, I would stick to LTS versions.

Move your /home to a separate partition (if it isn't already).
Install 16.04 but make sure you don't let it wipe your /home partition.
Apply any of your user customisations.

Wait until 18.04 LTS has been out for a couple of months before upgrading to it in 2018.
Ignore any 6 monthly releases.

Alternatively, install a rolling release like LMDE (which is a Mint/Debian amalgam) with an accent on stability.

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Thanks everyone who responded; illness kept me from the keyboard for a while there and I don't wish to appear ungrateful. I'll be following through and upgrading from disk (having first applied the cautions to protect data etc). Great forum. Thanks for the help :-)

What is the output of:

Having upgraded from version n-k to version n of Ubuntu (where k>1) by changing all references in /etc/apt/sources.list, let me just say that it isn't worth the effort. A clean install is not only cleaner, but also much faster.

Doesn't usually work like that.

You need to upgrade to n+1, then upgrade to n+2 etc.
If you stick to the LTS versions, you only need to do one upgrade every two years.
And you still get security updates and minor updates as they become available.