You can download the latest PowerCLI package here: https://developercenter.vmware.com/web/dp/sdk/55/vsphere-powercli
(PowerCLI 5.5 supports 5.1 and earlier versions as well)
You don't need to install anything in the GuestOS themselves unless you want to trigger the snapshot operation from within each GuestOS (which seems cumbersome).
Install PowerCLI on your workstation or some centralized management server to run scripts, you point the scripts to run against the vCenter server that manages your infrastructure. You will also need the respective permissions on the vCenter side to access the VM inventory, manage snapshots etc.
Just one hint: Make sure you don't overuse snapshots too much and clean them up in a timely fashion afterwards.