Changing the download location is not really possible at the moment, unfortunately. I'll add support for selecting between internal and external cards soon. In the meantime, you can change the download directory manually:

1.) Make sure gPodder is not running
2.) Edit /media/mmc2/gpodder/gpodder.conf and change "download_dir" to /media/mmc1/gpodder/ (or any folder you like)
3.) Move all folders (ONLY folders, not files) from /media/mmc2/gpodder/ to the new download location, so gPodder can find previously-downloaded files
4.) Start gPodder