Hey mahender1024,
The Long and Short of it is this:
Install SSO 5.5
Upgrade Web Client to 5.5
Upgrade Inventory Service to 5.5
Upgrade vCenter to 5.5
Upgrade any 3rd party plugin's like Update Manager, Syslog collector, SRM, ect
Upgrade hosts to 5.5
Upgrade VMware tools on all VMs to 5.5
Upgrade Datastores to 5.5
Upgrade your VM hardware level to 8-9, if you upgrade your VMware Hardware level to 10 which is 5.5's newest level you will ONLY BE ABLE TO MANAGER THE VM's THROUGH THE WEB CLIENT. So at the very least if your vCEnter server is Virtual leave this at 8 or 9 to prevent any configuration issues if vCenter has issues(AKA vCEnter is down, but how do I get to the webclient to fix it if its down?!)
Have a sandwich and call it a day 
Hope this has helped.