VMware launched the VCP5 certification exam on August 29th 2011, and they had given VCP3 and VCP4 holders a 6-month window in which they could update to VCP5 with little or no training requirement.
As of March 1st 2012, that window closed, meaning that from this point forward these are the paths to achieve VCP5:
Note that if you are a VCP2 or VCP3 holder that certification now doesn't qualify you for any form of VCP "upgrade" and you must take a full 5-day vSphere 5 training course.
VCP4 holders have the option of attending just the 2-day What's New training course, they can also take the 5-day courses if they wish but shouldn't need to do that unless they want a refresher of some of the fundamental vSphere features. The same applies to those who have attended training that would qualify them for VCP4 certification but have yet to take the VCP4 exam.