Hi Petteri,
I don't think you will get a step by step guide for that.
To achieve this you will have to create the custom text boxes and radio buttons, and then you will have to map these to the standard one's which are present in the next screen.
Go through below links they will give you some idea.
http://scn.sap.com/docs/DOC-35492
http://scn.sap.com/docs/DOC-54574
Regards,
Karthikeya