[Koha] how to update from 1.2.3 to 1.9.x

[Fayun Luo]

I have koha 1.2.3 installed recently. Now I want to update to 1.9.3. What
is the easiest way to do it?

If update is not possible, somebody tell me how to uninstall the koha
1.2.3 version.

Thanks a lot.
Kevin Luo