Hello, I am trying to update NetBSD 3.0 to the -current Version

I have read a lot of guides and documentation, for example:
http://www.netbsd.org/Documentation/current/#installing

Now, i am relatively current and ready to build your own current source
(the web says this).

But i have a problem: ./postinstall -s /root check  --> doesn't work

I am in a maze without any exit. I don't know what guide is the best.
Please, can you tell me the "best" guide or manual to update my NetBSD
3.0 to -current?
or give me some link? any advice?