[CentOS] Upgrade from 3.x to 4.x via yum

Sorry for the noob question.  I am trying to upgrade an older server from
3.x to 4.x via yum.  Yum is resolving the original 3.x repositories and does
not appear to be moving to 4.x due to the fact it still wants to use a 2.4.x
kernel.  

Do I need to point yum to another set of repos in order to upgrade versions?

Thanks

-jeff