Disconnect the negative battery terminal and wait for 10 minutes. That should reset all trouble codes, so you can start fresh. If the check engine light comes back on, (or any others, for that matter) you can have the codes read at any repair facility for little or no cost. Many times, the check engine idiot light comes on because some lame-brained gas jockey forgot to tighten the gas cap. Loss of pressure in the fuel system will fool the computer into thinking it has a problem with the fuel injectors, the fuel filter, or a myriad of other imaginary faults. I hope this helps.
You should use a diagnostic to make sure the trouble code problem has been handled first. Then if you need to reset the light, just unhook the battery connections and step on the brake pedal a few times to make sure any residual power in the system has been bled out, then hook up the battery connections again and start the vehicle. If the problem was taken care of properly then the light should remain off.