updating the price on change of the select list would require a custom ajax function to querythe database, then chage the price.
an easier way would be to add the increment to the select list, for example:
change:
<option value="<?php echo $row_rsSize['ProductOptionID']?>"><?php echo $row_rsSize['OptionName']?></option>
to:
<option value="<?php echo $row_rsSize['ProductOptionID']?>"><?php echo $row_rsSize['OptionName']?><?php if($row_rsSize['OptionPriceIncrement'] > 0) echo(" + ".$row_rsSize['OptionPriceIncrement']); ?></option>