Migration from 1.7.2 to the latest version 2.2 of CI

Hello, guys! I wanna clarify whether I need to do all steps from the instruction successively (I mean those steps http://www.codeigniter.com/user_guide/in...ading.html) or there is a way to migrate from 1.7.2 to 2.2 directly.
Please advise me.
I have already done the steps regarding v.1.7.2 to 2.0 migration in my project, but I got 503 server error. I can't find out what's wrong with it. I really love CodeIgniter and want to use its latest version for my project further...
Thanks in advance.