While you will need to upgrade the Creo version on your CAD worker for visualization, the Windchill server should support Creo 3 just fine.
http://support.ptc.com/WCMS/files/67180/en/CreoDataManagementCompatibilityRoadmap_02252015.pdf
http://support.ptc.com/WCMS/files/124498/en/PTCWindchillCreoSWCompatibility10x_2252015.pdf
Now if you are asking how to update a server installation of Creo itself, that is a different question.