I have Ubuntu 11.04 installed in my laptop and tried to upgrade it by opening the update manager and and making the necessary settings in settings - updates - release upgrade - normal releases and then hitting the check button. But nothing appeared indicating later version is available to be upgraded. When I run the following

sudo apt-get dist-upgrade

below is the result that appeared.

Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Also I am unable to watch YouTube videos in the Firefox 15.0 in my Ubuntu 11.04.