Open NBTExplorer, look for the name of the map, then open the regions folder in Nbtexplorer. Then search for name "Command" and value "gamemode". Once a result is marked, Double click it, then delete the content of teh textbox. Then strike "Find next". Repeat the previous step for 4 times (until there is no more search results). Finally, click "save" in Nbtexplorer, open your Minecraft and enjoy your Gamemode 1!