I just downloaded the iso image. That’s not a file that you copy to your DVD or Thumb Drive, but one you install as a bootable image. Unfortunately, it’s too big for a CD-ROM. It will have to be burned to a DVD-ROM.
You can download it from here: https://www.ubuntu.com/download/desktop. The next page will ask you to donate but you can use the link below that says to go straight to the download an not make a donation.
On the Ubuntu Web Site they say you need:
2 GHz dual core processor or better
2 GB system memory
25 GB of free hard drive space
Either a DVD drive or a USB port for the installer media
Internet access is helpful
If you don’t have any burnable DVD-ROMs you can use a 2GB Thumb Drive. I think those cost less than $5. There are all sorts of sites that show you how to transfer this image to either the thumb drive or DVD-ROM and boot your computer from it.
After you boot it will ask you if you want to install or try Ubuntu. Select “try” and it will boot your machine and give you access to all your hardware as if yo had booted to a hard drive. The only thing it won’t let you do is change any system settings or install new software. But it’s perfectly safe - you can run the programs and everything without changing your hard drive.
I actually have my laptop set up to dual-boot because I have to use Ubuntu to scan anything with my scanner. It was easy to install and is very easy to use.