Quick question, Can You flash an ESC without a computer? Can it be done with a programmer?
What earthsciteach was trying to say was: No.
You can program an ESC with a programmer. Programming is changing some of the ESCs options like "braking on/off", "low voltage cutoff on/off", "voltage limits", etc.. I think most ESCs allow you to change these settings by stick movements of the throttle. It is a little difficult because you have to wait for the right amount of beeps, move the throttle, wait for another beep and so on. To get around this you can use a programming card specific for your ESC model.
Flashing is something different. By flashing you replace the ESCs firmware - its basic programming if you will. This will usually result in a very different behaviour than just switching the options listed above.
You need a computer and the right adapter to be flash a new firmware.