Click to launch iTunes from the dock
Click to select Music from the list of libraries on the left
Select Preferences from the iTunes menu at the top left of the screen.
Select the General tab from the Preferences window then click the Import Settings... button.
Notice the Import Using dropdown.
Select the file format you would like to convert to from the dropdown. The iTunes default format is AAC. You can choose AAC, AIFF, Apple Lossless, MP3 or WAV.
Select your desired audio quality from the Settings dropdown.
Click the OK button to close the Import Settings Window. Click the OK button again to close the Preferences Windows.
Click to select the track you would like to convert then hold down the Control key then click the selected track to bring up its contextual menu.
Select Create MP3 Version to convert the audio file.
NOTE**: If you selected a different file format to convert to then the menu option would display the format you selected. ie Convert to *** Version
Notice that you now have two listings for the audio track in iTunes. The one with the most recent date is your converted file.
Drag the converted file onto your desktop or into a folder to copy it for use outside of iTunes.
You can now delete your converted file from iTunes by selecting it and pressing the Delete key.
Click Remove from the popup window.
Then click Move to Trash from the next popup window to completely remove the converted file.
Finally, don't forget to switch your Import Settings back to how you they were originally. Most likely using AAC. Follow steps 3-5 again and select AAC from the Importing Using dropdown.