What I have to modified to have one page registration?

This is how I got it done:

1. From Config>templates>Other, copy the SignUp.ascx into your own theme folder. (so it won't be affected by an upgrade)
2. Then remove/merge "[AS:CONTROLS:STEP][/AS:CONTROLS:STEP]", each "AS:CONTROLS:STEP" has a page, so if you want only one page/step, make sure you only have one "AS:CONTROLS:STEP" in the SignUp.ascx.
3. Change the "asp:button" text at the bottom of the page into something like "Register", "Sing Up", etc. (default is "Next")