The name may be misleading so let me quickly explain. When it says to complete bronze levels it means to complete the easiest form of the level, not get a bronze medal on the level.
Bronze games are the first tier of each game. They are the simplest to complete and are usually he easiest. Simply continue playing adventure mode until you’ve finished each of the mini games in the bronze tiers. There are 7 different mini games you can play and must complete. See the bottom of the guide for more info on these.