Dont open it with any text editor of any kind, if you accidentally edit anything in there incorrectly its not ideal. even changing the formatting can cause issues.
You need one of these Tactrix Openport 2.0
The application to open the file is ECUFlash which can be found here http://www.openecu.org/index.php?title=EcuFlash
Romraider is another great tool for editing the ROM and Logging the car
Given the level you are at, My suggestion would be get someone that knows more to flash the rom on for you. Then they can run some data-logging and ensure its doing the right things for your car. That being said if you want to learn more we all start somewhere so the other suggestion would be read a whole lot about tuning and logging before moving any further on making an actual change, then when you have a good understanding go buy a cable and start with just datalogging and understanding the current tune on the car...