How to upgrade from 1.2 to 1.4

Can anyone help me to upgrade from 1.2 to 1.4? I am not a UNIX guru:)

There are several distinct differences (at least in my experience) between 1.2 and 1.4. I just saved most of my config files, uninstalled 1.2, installed 1.4 and migrated over the important config files.

Thanks for reply.
I upgraded to freePBX 2.3.0alpha, now calls are droping. I do not know how to go back to asterisk-1.2 or freePBX older version.