Open Audacity. A new project window should appear on your screen. If you do not see a new project window, click "File" and "New" on the menu bar.
Click the "File" menu again and hover your mouse over the "Import" option. Select "Audio" from the list of media types that appears.
Select your MP3 file using the navigation window that appears on your screen. Click on the title, then click the "Import" button in the lower right corner. The MP3 file will appear as a horizontal series of waves in your project window.
Highlight your audio file by clicking anywhere in the left column of your Audacity window, beneath the time line. Your audio region should then turn purple.
Click "Effect" on your menu bar and select "Amplify" from the drop-down menu.
Click the indicator that appears on the "Amplification" bar, and drag it to the right with your mouse. The farther you drag it, the more your volume will increase. However, increasing the volume too much can result in clipping (distortion), so increase the volume conservatively. Click "OK."
Click the green "Play" button. If you hear any unwanted distortion, or if the green flashing peak meter in the upper left corner of your screen begins flashing red, click
"Edit" and "Undo" on your menu bar and apply the amplification again, this time with less increase in volume. Clipping can ruin a recording.
Click "File" and "Export" on your menu bar. When the pop-up menu appears, enter the name of the song in the "Save As" box and select "MP3 Files" from the list of options inside the "Format" box. Click "Save."