To view and edit your map settings you must go to the challenge you would like to edit, as map settings can be set differently for each challenge, which can be important if you are doing more than 1 at a time.
Once on your challenge, the map settings can be found near the bottom left of your screen between the locate button and the Google streetview button.
From the Map settings page you will be able to adjust three things:
Map Style - Classic, Terrain or Satellite (your choice will now also remain saved until you change it again)
Visible people - here you can control the groups of people you see on your screen. Read more here.
Pacemarker - When you select your timeframe for a challenge a pacemarker will move daily along the map to represent the required pace to achieve your goal. Some people prefer not to have this, so you can switch it on and off. (Please note, there is no consequence for the pacemarker "beating" you to the finish line, you will still be able to post distances after that point as long as you are within the 18 month timeframe for completing challenges.