All required commands are listed in my tutorial.
Update/// oh, I just noticed that datasheet says it has different power output values but gives no command to set it.... For HM-13 the signal power AT command is AT+POWE<value> (0, 1 or 2), but it doesn't work. Also set AT+MTUS1 command for higher data packet transmission and AT+HIGH1. And don't cover antenna with steel parts (steel is very bad for signal, even aluminum is better), also try to place the module far from Ground wires.