How to find out which version of Ubuntu

From a Terminal (Applications → Accessories → Terminal)

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04
Codename: precise

And to find out if you are running a 32 or 64-bit OS.

$ uname -a
Linux magnus-HP-ProBook-6550b 3.2.0-24-generic #37-Ubuntu SMP Wed Apr 25 08:43:22 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

For 64-bit you will see: x86_64
and for 32-bit: i686