Install OpenSSH SFTP client to Windows 7
There's Microsoft Win32-OpenSSH project.
It can be manually installed to any version of Windows.
For client tools, just extract OpenSSH-Win64.zip (or OpenSSH-Win32.zip) anywhere you want. No "installation" is needed.
Note that for Windows 10 version 1803 or newer, OpenSSH is already built-in. On older versions, it's available as an optional Windows feature. Just go to Settings > Apps > Manage optional features and add "OpenSSH client".
It installs to C:\Windows\System32\OpenSSH (and is added to PATH).