I have a 2001 Buick Century.
Took it to the Sears store - and had 4 Michelin tires put on Friday.
Saturday, the low tire light on the dash is lit. I have had the air checked -
All 4 tires are up to the right pressure. However, Low Tire Light is still glowing on the dash.

What can I do ? Should I return to Sears? What caused this?

Look in your owners manual for resetting instructions. In a 2000 Impalla, it's reset using the radio and so is a whole bunch of car options like how the headlights and autolocks behave and resetting the change oil and tire pressure warnings. The air in the tires has to be correct for the tire reset to work.

I believe is can also be reset using the OBD II diagnostic connector and a scan tool.

Those cars that have transmitters at the tires require a specific deflation/inflation sequence.

There should be a reset button in the fuseblock. Turn key on push and hold button for 5 seconds until light blinks in dash. Needs to be reset anytime tire are changed or rotated or pressure changed. This old style system uses the abs wheel speed sensors to determine if a tire is low and is not very accurate. False light coming on is common.