[How to change the ships little icons in map view?]

Hi all,  newbie here...  I can't find a way to change the little icons of my ships in map view  (the ones you use to command/give orders to your ships)    some of my Icons look ok, but others just show a big grey round icon.  so when I select one of those  a can't really see if  it is selected (highlight white circle) ..

 

Any help would be appreciated.

 

Thanks all and have fun.

 

Reg