var currentid = 1;

function changePic (picid) { 

   var whichpic = document.getElementById(picid);  
   var whichlink = document.getElementById(picid*10);
   var currentpic = document.getElementById(currentid);
   var currentlink = document.getElementById(currentid*10);
   
   if (picid==currentpic) {  
   } 
   else { 
      currentpic.className="hidden";
      currentlink.className="hidden";
      whichpic.className="shown";
      whichlink.className="shown"; 
   } 
   
   currentid = picid;
}