My daughter got a computer at a yard sale with an old version of ubuntu. When I try to update, it asks for admin password. It also says version no longer supported.
4 Answers
I would suggest downloading an ISO on a working computer and just re-installing Ubuntu. Who knows what kinds of problems you may have inherited with a used machine.

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This is kind of a two-pronged question, but it can be answered with one solution.
The solution would be to install a newer version of Ubuntu. When it says "Version no longer supported", it means the version of Ubuntu that is installed has reached its End of Life, that is to say no more updates will be provided.
I would install either 10.04.3 LTS or 11.10. This would wipe the data on the old system, replace with new passcodes, and allow you to update the software.

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I'd definitely recommend doing a clean install of Ubuntu. Grab the latest at ubuntu.com, put it on a CD (with Brasero, which is probably already installed on the computer), backup your stuff, and reinstall.

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An older computer may or may not work with a fresh install of Ubuntu.
The safest option would be Ubuntu 10.04.3 LTS, but would need to know exact hardware to know better.
Two solutions:
Option A. If the computer is already running Ubuntu 10.04.3 LTS (or 10.04.x), then just replace system password. If the Ubuntu version is earlier, stick with option Option B.
see: How do I reset a lost administrative password?
Then do the updates, and see how well computer is performing. Take a note of which drivers, devices, and applications are installed. If all is well, you can proceed with a fresh install (Option B).
Option B. Create an install CD or USB, for Ubuntu 10.04 LTS, and install.
Proceed with install, erasing (and replacing) ANY existing OS, software, or data on the PC.
Once you have successfully installed and are using Ubuntu, you can experiment with testing (but not installing) the latest version: Ubuntu 11.10
(again, the merit of this would depend on your hardware specifications)
shred -n 50 /dev/sdb
for instance. But I would do that out of paranoia more than anything else. – jpaugh Dec 03 '11 at 22:00