Hi,
first you need to install the Update Manager Server ( can be installed on your vCenter Server ). The installer is on the vCenter Server Image.
After that you connect to your vSphere Client to the vCenter Server, click on plug-ins -> manage plugins and download and activate the Update Manager Plugin on your Client.
Here's a link to the Update Manager 5.0 installation and administration guide: http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vsphere-update-manager-50-install-administration-guide.pdf
Regards