How to prevent dropdown option and maintain the selected opt

Question

<select class="form-control" id="QP_1" onchange="OnChangeQP(this.id)">

<option value="1">All Products</option>

<option value="2" selected>Selection</option>

</select>

 

i want to change the option selection to all products at the i don't want change all products i need to maintain selection option dropdown.

 

please help me.

thank you.