Hi Khan ,
Upgrading steps is given below for your help ...if it is helpfull please mark my answer as helpfull or correct ..Thanks.
1. We have vCenter Server appliance 5.1 with latest build in our environment. To upgrade this vCSA 5.1 to vCenter server appliance 5.5 Update 1, Download and deploy the vCenter Server Appliance 5.5 Update 1. Take a look at the post Download link for vSphere 5.5 update 1 and other softwares.
2. Once you have deployed the new vCenter Server appliance. Let it leave with the DHCP address. Connect to your new vCenter Server appliance admin page using the below format of URL
At the first time when you access the vCSA appliance , vCenter Setup wizard will start. Select the option “Upgrade from previous Version” and click on Next.
3. During this step, We need to exchange the keys between both the new vCSA (5.5) and old vCSA (5.1) appliance. To do this, copy the key that is generated from vCSA 5.5 and paste it in the import dialog box of the old vCSA 5.1 appliance.
Again copy the key generated on old vCSA appliance (vCSA 5.1).
4. Click Next, and choose to generate new SSL Certificates
5. Type the SSO admin password. You can use the same password which was used for early version.
7.Below page will displays the hosts which are managed by older vCSA 5.1. Select the hosts from the list which want to managed by the new appliance.
8. vCenter upgrade checker will report any host problems that may be preventing an upgrade.
9.It will always recommended to take backup or snapshot of your virtual machine before proceed with any upgrade. It will be helpful to recover your VCSA appliance if in case upgrade failed. Select the checkbox “I confirm that i have made a backup/snapshot of the source vCenter Server Appliance and the external database” and click on Next.
Once upgrade is completed. vCSA 5.1 appliance will shutdown and new appliance vCSA 5.5 will reboot and it will configured with the same IP address and data of old vCSA applia
