Can we upgrade a Single cell vCloud environment from 5.1 to 5.5, considering we can have a downtime available for the whole environment.

I have a single cell environment for vCloud director 5.1. I am planning to upgrade it to vCloud 5.5,  Can anyone help me with the steps, considering the fact that I have the downtime of the environment.

What concerns me is  How my environment will behave if I will upgrade the vShield Manager, as the vCloud database will not be able to update If its not powered on.