Re: Updrading from 4.1 to 5.1

You can directly go for a latest version available of vcenter and esxi from 4.1. For your easier reference, I have copied the link of the KB article below which would help you to upgrade the vcenter and esxi hosts

Download Vcenter 5.1 :

https://my.vmware.com/web/vmware/info/slug/datacenter_cloud_infrastructure/vmware_vsphere/5_1

Download ESXi 5.1 :

https://my.vmware.com/web/vmware/info/slug/datacenter_cloud_infrastructure/vmware_vsphere/5_1

Upgrade ESXi 5. 1 :

http://kb.vmware.com/kb/2032757

Upgrade Vcenter to 5.1 :

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

  http://kb.vmware.com/kb/2021193