Uploading Images To Twenty Ten Header Using Filezila

Like many people I’m having trouble uploading images and receiving the message ‘Missing a temporary folder.’
There seem to be many solutions (too complicated for me) put forward for this.
Can I simply upload an image to the header images file using Filezilla? I’ve tried to do this but still cannot get access to the image, what am I doing wrong and how do I do it right?