I am new at this site. I would like to ask you something that i am not sure about for the update to 14.04 LTS from 12.04 LTS. The upgrade manager has notified me that a new version of ubuntu is available (14.04). What i am not sure about is that i dont know if the update will delete all my files from my desktop when i'll install it! i would appreciate if you could offer me some help with this!
Well, software upgrades shouldn't touch your personal files. Software upgrades try to go with old configuration files, but not always. You should be fine, but me personally, when looking at transitioning dozens of important packages, I'd still wonder if a fresh install isn't too far off, so I'd backup my stuff anyways.
An LTS to LTS upgrade will focus on upgrading Ubuntu to a more current version and try and make use of old configuration files, your home partition should be left alone as it is personal data. That is if the upgrade is successful sometimes it can go wrong but this does not very often. I strongly recommend backing up your files on a external hard drive before upgrading. Next download the ISO and burn it to a disk use that to upgrade from 12.04 LTS to 14.04 LTS. That way if your upgrade fails, you have a Installation CD to use in order to try again and your data can be loaded onto your computer from the external hard drive.