I'm going to install Ubuntu 12.04 Precise Pangolin(x64) and this article says it requires clean install from 32 bit. Does it mean — forgive me, I'm Turk and my English is not perfect — "First install 32 bit and then install 64 bit onto it?"
Ubuntu – Is 32 bit Ubuntu installation necessary to install 64 bit Ubuntu
32-bit64-bitinstallation
Best Answer
You do not need to start with a 32-bit installation to get a 64-bit installation.
In fact, you really can't convert a 32-bit installation into a 64-bit installation. "Cross-grading" is unsupported and all existing methods for attempting it are likely to leave you with a poorly functioning system that contains some 64-bit and some 32-bit components.
If you want to install the 64-bit version of Ubuntu, just install that. Having the 32-bit version installed first will only complicate things, as you'd have to remove it or install over it.