The vCenter 5.5 installation bundle can be downloaded from the VMware downloads page for vSphere.
We can use the following steps to download vCenter 5.5:
Go to the downloads page using the URL https://my.vmware.com/web/vmware/downloads.
Click on the Download Product hyperlink corresponding to VMware vSphere.
On the Download VMware vSphere webpage, locate VMware vCenter under needed license.
Click on the Go to Downloads URL corresponding to the vCenter entry to reach the web page titled Download VMware vCenter Server.