Install a Spigot server, it will be used as a base for your new server.
Connect to FTP
Connect to your FTP server - How To Edit Files Using FileZilla FTP
Delete all files from your Spigot server except server.properties and eula.txt.
Upload your new server files from your PC to your server on our hosting (don't overwrite files server.properties and eula.txt)
Rename your game server JAR files to server.jar