How to update a contact field with vb.net ? #5

Hi,

I would like to update a field in contact, but I can't see the way to do that. Would you give me a hint please ?
According to the existing code, I would like to do something like this
contact = UpdateContact (contact as contact, Field_Name as string, Field_Value as string)
where Field_Name could be FaxNumber for example, and Field_Value could be a string value.

Any help or tips is greatly appreciated.
Thank you