Change selected value of kendo ui dropdownlist

You have to use Kendo UI DropDownList select method (documentation in here).

Basically you should:

// get a reference to the dropdown list
var dropdownlist = $("#Instrument").data("kendoDropDownList");

If you know the index you can use:

// selects by index
dropdownlist.select(1);

If not, use:

// selects item if its text is equal to "test" using predicate function
dropdownlist.select(function(dataItem) {
    return dataItem.symbol === "test";
});

JSFiddle example here