3. You start a message thread in the forum, for discussing the change. In that forum thread, you also point to #4 & #5, below.
4. You post a pick with an end date, asking users to vote to keep the original icon or to change to the new one.
5. You post a pick with an end date, asking users to vote to keep the original banner or to change to the new one.
Note: the end date should be long enough to allow for enough fans to respond, but not ongoing. 2-4 weeks is probably good.
6. If the users vote to make a change to the icon and/or banner, send a message to the staff (using the "contact us" feature) with:
a) the name of the club
b) the URL(s) of the completed picks, showing that users wanted the change
c) the URL of the new icon
d) the URL of the new banner
7) The staff makes the change.
Just as an aside: having a consistent look to a club - particularly with regards to the icon, not so much the banner - is considered by many users to be a good thing, since the icon visually represents the club, and any change to a club's icon creates a lot of confusion for users across the site who then can't as easily identify the club. So that may explain the resistance you may find in picks against change. Still, if a majority of the users who do pick vote to make a change, it's all good.