I'm currently using Ubuntu 12.04 LTS and wanted to upgrade using the 14.04 LTS ISO.
Thanks in advance guys :)
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If you burn the ISO image and boot with the DVD created, you'll be able to perform the upgrade. You just have to select the option for upgrading your current installation of Ubuntu 12.04. Your data will be kept and the setup process will try to reinstall the packages installed (even external ones), if possible (of course), at the end of the install process.
It is even possible to upgrade from a 32-bit edition of Ubuntu 12.04 to a 64-bit edition of Ubuntu 14.04 that way. Of course, in that case, no previous package can be reinstalled...
Of course, it is not booting from the ISO itself (see Solution 2 below).
If you have an USB external drive with virtual CD/DVD feature (some enclosures like Zalman ZM-VE300 allow that), you'll be able to boot on the ISO image mounted as if it was a real CD/DVD.
You can create an USB boot disk from the ISO with "Startup Disk Creator" which is included in Ubuntu by default. Just type "Startup Disk Creator" in the Dash.
If you want to upgrade Ubuntu 12.04 to Ubuntu 14.04 without waiting July 2014, you can also use this command line in Terminal:
However, the ISO won't be used in this case. Everything will directly be downloaded from Ubuntu repositories.
Don't forget to backup your data before performing any upgrade. It's always better to have a backup even if you don't have to use it than having no backup when you really need one ;-)!
Even you can upgrade without ISO image, so need to delete 12.04 and reinstall 14.04. so need to download all application,application data again in 14.04.
follow the following steps:-
First things first: make sure that you are fully up-to-date. Double check by opening the Update Manager application from the dash and installing all updates listed.
When that’s done, open the Dash again and launch the Terminal application. When it opens click inside the window and type the following command carefully:
Hit the enter key and, if prompted, enter your user password.
The Update Manager application will open after a few seconds with a prompt to upgrade. Click to begin the process.
NOTE:- Your system should to connected to internet. If using laptop Keep in AC mode.