AdWords API Problem updating Keyword maxCPC

I am trying to update the keywords maxCPC property using VB.Net. I am
able to change a Keyword's destination URL using a criterion object.
Unfortunately the criterion object does not have a maxCPC property

The documentation recommends using the Criterion service to update
Keywords, passing a keyword object. I do not see how to pass a Keyword
object to this method. I am only getting the option of a criterion
object.

Am I missing something obvious here?