sFTP is part of OpenSSH. OpenSSH is used to securely connect a client to a server, so you may make modifications to the VPS.

However, it also has a function where you can upload securely using sFTP (Secure FTP). For sFTP you will need to ensure that you have enabled or already have "shell access" to your account. Once that is established, simply go ahead and upload your files securely using sFTP.

A great application to use for sFTP is FileZilla and can be downloaded online free of charge.