You mean in the forum? Uploaded level cards themselves cannot be changed. You can only change the name of the level card that is displayed in the forum and the description of it. To do this, simply go to the media page of your level card and tap the pen button in the bar up there. Then the above entries can be changed. If you want to change the uploaded level card (PNG file) yourself, only delete it and upload it again. I hope that answers your question.
