Open your audio editor and drag the multi-track audio file into the main editing pane. Some programs may require you to use the "File" menu and select "Import Audio" from the drop-down menu.
Select the vocal track by clicking once on the track title. In the "Effect" menu, select "Amplify" and drag the slider to right. The further you drag the cursor, the louder the track will become. You can select the "Preview" button to listen to the audio before confirming changes. This makes it possible to ensure you have selected the right volume. Press "OK" to adjust the track volume.
Choose the "Effect" menu again and select "Compressor" from the drop-down menu. Leave all of the options at the default setting and click "OK." The compressor will help to even out the audio and balance the high and low frequencies.