Click on ''Settings'', then ''Easy Mode'' in Personalisation, then select ''Standard Mode'', the icons should have reduced in size, hope this works as well as it did for me, found the answer on my S3
Select ''SETTINGS'', now select ''EASY MODE'' in Personalisation, now select ''STANDARD MODE'', the icons on the display will now reduce in size. I hope this works as well as it did with my S5, I got the idea from my S3.