Upgrade existing Libreoffice to Libreoffice 4?

I have dowloaded Ubuntu 12.4.4 (PP) but I want to upgrade the existing Libreoffice to Libreoffice 4. How do I do that?

Install LibreOffice from PPA. See details: LibreOffice-4-2 PPA for Ubuntu 12.04 / 13.10 - How to install - Tutorial