Hello,
can any one tell me what is the basis difference between Ubuntu and Fedora... Is there any enchancement in new version? What about security, any chanages in that?
There's some great enhancements in both new versions of Fedora and Ubuntu ... including security. Always worth a read of their news releases on their respective websites.
If you're interested in Fedora - you could also take a look at Centos.
If you're interested in Ubuntu - you could also take a look at Debian.