http://www.electrodragon.com/w/ESP8266_ ... d_firmware
When you are flashing firmware ensure that GPIO-0 is pulled low for flash mode and left floating for normal operation. I.e. disconnect power, pull GPIO-0 LOW, connect power and flash firmware. For normal operation disconnect power, ensure that GPIO-0 is not low and power up.
If you are comfortable with the command line then I would recommend esptool for flashing:
https://github.com/themadinventor/esptool