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You can edit the podcast information by right clicking on it and choosing "Get Info."
The following articles will provide more information:
Editing and arranging content
Each audio or video file in iTunes has several settings and tags that can be easily modified. These options can be accessed by selecting any file in the iTunes browser windows and selecting "Get Info" from the File menu. You can add song lyrics, artwork and set special playback options. The "Info" tab lets you edit information about the file including artist and album info.