Welcome to the forum.
How to get help on the Dynamo forums - FAQ - Dynamo
What have you tried so far? What options have you looked into? What categories are the existing families? What category do you want to change them to? How are you loading the families? Are there any additional settings that need to be taken into account for the new category (or replaced from the old category)?
Basically, you need to look at how you would do this manually and then how you would automate each of those steps.