Re: what are the steps and best practices to upgrade vSphere 4.0 to 5.1?

Thought it was explained above i would like to add this guide for your reference in case you need it .

http://pubs.vmware.com/vsphere-51/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-51-upgrade-guide.pdf

it will tell you everything you need to know about the upgrade .

Let me know if you need anymore help .

Regards