No need to ground it by wire. In order to get the the board into "download mode" you need to 1) connect the board to the computer; 2) press/hold the button labeled as 0; 3) press and release the RST button; 4) release the 0 button. After this sequence a new serial port should come up in your computer. After flashing the board just remove the power and plug it back and it will be done.