You can edit the size of all OS elements in one go with DConf Editor, a graphical editor for a whole pile of system settings.
It is available in the repositories, so you can type in the following command or else get it from the Ubuntu Software Centre.
Once you've got it go to the "org" section in the left hand margin then look for: gnome > desktop > interface > text scaling factor.
sudo apt-get install dconf-tools
Default value is 1.0, if you make it bigger (say 1.2 or even 1.3) everything will get bigger, and if you make it smaller (say 0.9) everything will get smaller. Don't put it at 5 straight away or everything will be unusable