pg_upgrade doesn't work?

So why does the documentation tell me that I should use the pg_upgrade
command to migrate my 8.4.20 db to 9.6, but when I run the command it tells
me that the major version is different so it won't run?  Is there some kind
of issue with the location of the execution binary?  

Mark Cogan
Systems Administrator - Contractor, Code 3030
Information Delivery Systems, Inc
Onsite - Naval Research Lab
(202) 404-2032