Change quality on recorded shows???

Is there a way that you can change the quality on previously recorded shows? I have my Humax setup just as default, so it records everything on high. When it recorded a few movies that I want to put on DVD, I found out they were just over two hours, and want two DVDs. Beyond re-recording them, is there any way to convert them so they'll record on one DVD.

I saw something about DVDShrink, but how do you get the recording to a PC to shrink it?

Thanks,

Terry