Step 1 : You have to copy this two files to your Theme in the adminhtml
app/design/adminhtml/default/default/template/sales/order/shipment/create/tracking.phtml
app/design/adminhtml/default/default/template/sales/order/invoice/create/tracking.phtml
Step 2 : Open : app/design/adminhtml/default/default/template/sales/order/shipment/create/tracking.phtml
(you will find this code at Line number 93)
Replace with
<select name="tracking[__index__][carrier_code]" id="trackingC__index__" class="select carrier" style="width:110px;" disabled="disabled">
<?php foreach ($this->getCarriers() as $_code=>$_name): ?>
<option value="<?php echo $_code ?>"><?php echo $this->escapeHtml($_name) ?></option>
<?php endforeach; ?>
</select>
Step 3 : Open : app/design/adminhtml/default/default/template/sales/order/invoice/create/tracking.phtml
(you will find this code at Line number 93)
Replace with
<select name="tracking[__index__][carrier_code]" id="trackingC__index__" class="select carrier" style="width:110px;" disabled="disabled">
<?php foreach ($this->getCarriers() as $_code=>$_name): ?>
<option <?php if ($_code=="ups"): ?>selected<?php endif; ?> value="<?php echo $_code ?>"><?php echo $this->escapeHtml($_name) ?></option>
<?php endforeach; ?>
</select>
