Hi Joao,
I cannot find the delete function either!.
If you make a mistake with Ubuntu, the beauty of the system is that you can re-install without losing your data if you do it using the "Something else method", I re-install all my favourite apps using a terminal "Meta" command like the following example:
sudo apt-get update && sudo apt-get install synaptic shutter gparted gpart xsane hplip-gui deluge pepperflashplugin-nonfree bleachbit libreoffice me-tv kaffeine linux-firmware-nonfree unetbootin devede handbrake libxine2-all-plugins transcode ubuntu-restricted-extras vamps videotrans playonlinux mono-complete p7zip-rar winbind kshisen amarok kontact skype faac flac chameleon-cursor-theme clamtk mate-desktop-environment-extras alien k3b chromium-browser nvidia-current
The above command will install (almost) everything I need without me having to think about it, it takes a while but you can drink a coffee while it is happening, I only have to take note of one licence agreement when running the command!. 
The above command is also an example of my preferences, each person needs to decide what they need, some of the packages I choose may be bloat to others, the important thing to remember is that when you create your meta command, make sure you type the exact name of the package or it will fail!!.
RESTART AFTER RUNNING SAID COMMAND!.