Menu: View→Analysis Properties→Estimation→Estimate means and intercepts
When Estimate means and intercepts is checked, means and intercepts are estimated, and you can constrain them. (See To constrain parameters.) If you leave Estimate means and intercepts unchecked, means and intercepts will not be estimated.
Programming
In Amos Graphics programs, you can put a check mark in this check box by using the following statement (Visual Basic):
pd.GetCheckBox("AnalysisPropertiesForm", "MeansInterceptsCheck").Checked = True