How you enable SSH/SFTP will depend on the operating system.

Please note, putting any computer on the open Internet is dangerous. It is important to understand how to secure the system. If you are hacked you could have serious issues. Especially if you are using a system with critical IP or financial data.

If this is a business operation, you may consider finding a professional. opening firewall ports and hardening servers is a fairly technical undertaking. You can do it, but it will require a great deal of study if you have limited experience.

Another option is to find an SFTP hosting site to move the files. But that triggers the issue with security that you have with email.