Install VitaShell on your PS Vita
Open VitaShell on the PS Vita
Press Select to start the FTP server
Note the FTP address shown on the screen
Install and open WinSCP on your PC
Set File protocol to FTP
Enter the PS Vita IP address in Host name
Set the Port number shown by VitaShell
Click Login
Use the WinSCP file browser to transfer files
Drag and drop files between your PC and PS Vita
Press Start on VitaShell to stop the FTP server when finished