How to iterate over 25 Sprite Objects (Unity 5 - C#)

I wanna show a minimap on the screen. The minimap would look like this (bottom right corner, this was done time ago in Visual Studio):

Have two problems with that, I have 25 Image objects created in the scene and 25 in the playercontroller script:

public Image minimap0, minimap1, minimap2, minimap3, ... , minimap24; 

but I can't make to change its sprite, and also, I don't know how to change all 25 objects sprite with a "for" loop (the foor will look like this http://imgur.com/qfi1Ht1 ).

The map is stored in an array for checking positions.