How do you edit the parameters passed via a custom action?

How do you edit the parameters passed via a custom action?

when building a custom action, I built a function via the 'wizard' to pass 3 parameters.  I need to change the type of the Argument from Int to String and it wont let me edit the types. I want to change the sub-rev type below.  You cant change it by clicking edit,  How do you do this?