240 v to 120 v. Just changing the plug probably isn't enough.

Any given motor running at 120 v will need twice the current as it needed at 240 v. So that is probably why it tripped the circuit breaker--it is drawing too much current. If it really is dual voltage, I'm guessing there is a switch on the motor you can change or a wire (or two) you can connect/disconnect/swap that will allow it to run on 120 v without drawing as much current (but it will be slower or have less power than it would at 240 v--you can't cheat physics).

Did it come with a manual? Can you Google the model number and get instructions?

If none of that made any sense, then I would recommend getting an electrician (hopefully you know someone, because it is probably a very quick fix and you can get away with paying a plate of cookies or maybe a steak for the help).