You can switch the type of node within that node type at any time. This means that you can easily switch between different kinds of Inputs, Actions, Values, or Results. You cannot convert an Input to an Action or Result, or vice versa. Simply click on the dropdown (which also displays the current active Node type) next to the name of the Node above the content editor. Once you click on it, a list with all possible Node types appears. When you click on it, the Node type changes.
Change the type of Input
Change the type of Value
Change the type of Action
Change the type of Result