In Java Tutorials there are examples how to convert legacy code to use generics:
http://docs.oracle.com/javase/tutorial/extra/generics/convert.html
Java Generics FAQ also has the subsection about dealing with legacy code:
http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#Coping%20With%20Legacy
Without examples it's hard to give you something more specific.