basically in whatever program that you are using to edit the file, hit the find/search option within that program to find the particular line that you are looking for.
In this case, you are looking for "if (can_administer('canadminstyles'))".
Then once you find this line, you have to copy the second part and add it above this code depending on the instructions given. So in this case or particular example that you have used, the final code after editing should look like this,
Code:
construct_nav_option("General Settings", 'arcadeadmin.php?do=general', '<br />');
construct_nav_option("Game Settings", 'arcadeadmin.php?do=games', '<br />');
construct_nav_option("Score Settings", 'arcadeadmin.php?do=scores', '<br />');
construct_nav_option("Challenges", 'arcadeadmin.php?do=challenges', '<br />');
construct_nav_group("Arcade", '<hr />');
if (can_administer('canadminstyles'))
hope that helps, if you still need help just ask