Edit in JSFiddle

var obj = {
  aa: 11,
  bb: 22,
  cc: 33
};
for(var i in obj){
  var temp = obj[i];
  delete obj[i];
  var str = i.replace(/^.+$/g,
  function(matched) {
    return matched.toUpperCase();
  });
  obj[str] = temp;
}

for(var i in obj){
  $("body").append(i + ": " + obj[i] + "<br>");
}