When you first get your server, you can log in to your Linux based VPS server through SSH with the program PuTTy (Download Here) and enter in the IP address and port received in your welcome e-mail. Once logged in, there are a couple of initial commands that you can run to update and upgrade the Operating System that your virtual machine is provisioned with.
To update and upgrade a Debian based system (Debian & Ubuntu):
To update and upgrade a Red Hat based system (CentOS, Fedora, RHEL):
This will upgrade and update all of the packages on your VPS to make sure that there are no security issues caused by out of date software.