Exactly like Neil said, desoldering pump, or perhaps solder wick. You can make your own if you don't have some with some copper wool, if you don't have that steel wool and flux works. You just stretch out a piece that is about as big around as the graphite in a pencil, and roll it a little, heat it on the solder and the solder will leave to the wick as it 'soaks' it up. Could also just use the bump method, just heat the glob and flick or bump the board in a way that it'd make the solder fall off.
Before giving the ESC power make 101% sure nothing is bridged, if something is it may cause the ESC to catch fire. Next time don't add so much solder
To help avoid adding too much tin both places, and then touch the wire to the pad in the correct position (centered and not touching) then heat the two with your CLEAN and TINNED soldering tip, you want to clean the black off and then lightly tin the tip. Gives better thermal conduction.