Vcenter ugprade from 5.1 to 5.5

I'm running vcenter 5.1 on my test environment.(SSO on separate server,Webclient and vcenter on separate server,Inventory service on separate vm).what is the best method of upgrade this to 5.5.As I understood, i ve to follow below steps.?

1. Upgrade vCenter Single Sign-On.
   
   
   
   
2. Upgrade vSphere Web Client.
   
   
   
   
3. Upgrade vCenter Inventory Service.
   
   
   
   
4. Upgrade vCenter Server.