Get out of the game completely and then instead of going back into the game, while the game is selected instead of loading it, click the button with 3 lines on to go to the manage game and settings (or something like that). Once you are there on the left, go into saved data and on the right side of the screen you'll see your Madden profile and under that should be "reserved space". Move over to that on the right and select it and then delete it.
Boot the game back up and try your download again. If it works, download everything you need or you'll have to do that again next time you want to download something from Madden share.