I have a concord 80 plus gas furnace and the red light blinks four times indicating that the high limit switch is on. Is there anything I can do to fix it myself?

Make sure the air filter is clean & not highly restrictive (pleated 1"). Check for blocked or closed vents. Check the blower wheel to verify it is clean.

Yep, first step is checking/changing the furnace filter/s. Let us know if that does the job. If not, let us know and we will take the next step.