This brief HOWTO shows how to take a working 32 bit 14.04 installation and convert it into a 64 bit system. You will be able to keep all your programs, settings and data. You start with a 32 bit system that can run 64 bit programs, then convert it to a 64 bit system that can run 32 bit programs.
With the release of Ubuntu LTS 14.04 (Trusty Tahr), the ability to use the multiarch facility to upgrade to 64 bit is easier than ever. Much simpler than upgrading 12.04 and an evolution of upgrading Debian 7 or 8.