how to reset smc?

My DVD/CD Rom player is not working, it spins, makes a 'whirring' noise and ejects the disc. The problem was sporadic at first and then became permanent. The main suggestion on other discussion threads are to either clean the drive or reset the SMC. I just purchased a cs/dvd lens cleaner and the drive ejected the cleaning disc. I am seeking information on how to reset the SMC.