To begin with it's always best to test your original consoles sound works. It isn't always required, as you have have a dead speaker, but if your console works first its a good sign.
STEP 1. Open up the Game Boy Advance using a Triwing screwdriver by removing the 6 screws on the back, and 1 more philips screw in the battery compartment.
STEP 2. Once inside, it is easier to also remove the main circuit board from the shell by removing the 3 philips screws from the centerline of the motherboard (one to the left side, 2 to the right side above power slider switch. Before lifting out the console, push the tabs on either side of the ribbon connector at the top towards the top of the shell. This releases the pressure on the ribbon cable and you can pull out the cable, leaving the screen stuck down in the front shell. Now remove the circuit board from the shell.
STEP 3. Remove the old speaker from the front PCB by cutting or desoldering the speaker wires.
STEP 4. Solder the pads on the Game Boy Advance to the pads on the CleanAmp as shown.
STEP 5. Be careful when soldering the CleanAmp pads that you do not short the pads together or remove the resistors or capacitors near the pads.
STEP 6. Solder the two wires on the top right of the CleanAmp to the speaker wires. Polarity doesn't matter, you can solder either wire to either side.
NOTE: The Dehum Dehiss Kit is strongly recommended to remove the audio noise from the board.