What you'll need to do the job:
A catch bottle, clear plastic tube, new brake fluid, Phillips or flat head screwdriver, wrench, and someone to help, if needed.

When brake fluid gets dark and dirty - normally it is a clear/pale yellow, you need to bleed the brakes to replace the fluid and prevent brake fade. Brake fade is when you have no hydraulic effect because the fluid breaks down and is no better than water. Otherwise, do this procedure at least once a year.

First, uncap the brake fluid reservoir. Pump the front brake quickly 3 times and then hold. Have your helper open the bleeder screw (check owner's manual to find location on your bike) to drain brake fluid. Once the bleeder screw is opened, the brake lever will sink all the way to the handgrip. When it does that, close the screw and only then let go of lever to ensure that no air gets in the brake line (or brakes will be spongy and you'll get brake fade). Then pump the lever 3 times until pressure builds up in the line and repeat the above steps. Use a small hose from the bleeder screw into a bottle to catch the dirty fluid. As you bleed out the dirty fluid, add new fluid to the reservoir until the brake line is totally flushed with new fluid. Once you get the hang of the process, it should work in a nice rhythm.