You are missing the statement in your script that would set the screen field to the new value. So after setting the otext variable with the IFs, you need something like
session.findById("wnd[0]/usr/txtPersonas_2").text = otext;
There is no Refresh Screen statement in version 3.0 since it's not needed.
You can find scripting documentation in the Personas Knowwledge Base at Personas Knowledge Base - SAP Imagineering - SCN Wiki
This is part of the Screen Personas Portal which is also available directly from the Personas 3.0 editor by clicking on the Help button.