Select the section of the recording that you want to make louder by dragging over the waveform in the display.
Right-click on the highlighted section and select "Process," then "Normalize," or find the "Normalize" option in the Effects menu.
Move the slider toward 0 decibels or type a higher number in the box, then click "OK." You should always be starting from a negative number, so moving toward 0 will increase the volume.
Return to the main screen and observe the effect on the waveform. You will be able to tell at a glance if you've made it louder because the waveform will be bigger.
Repeat steps 2 through 4 until the sound is at the desired level.
Drag over the entire track and normalize it to a standard level if you want to equalize the left and right channels and get an even level of volume across the song.