You'll probably have to get into the service menu. In my opinion it wouldn't be worth it for a 2% overscan, which is on the low side.
Does your set have a "dot dot" mode that allows you to turn off the overscan for PC input (assuming you have one). If so, see if you can turn it on with other inputs.
Oh, if you have a "dot dot" mode and you have a DVI connection you might be able to use a DVI to HDMI adaptor/cable for your set top box/DVD player if it really bothers you that much.