Apple Logic Pro /LogicExpress Discussion

I am a tyro at Logic, can someone explain how to change midi tracks to audio track.  I have Superior Drummer using multi-channels, so all of the sounds of the drum kit, i.e. snare, kick, hi-hat, toms, cymbals, overhead mics, and room mics have their own track.  I am trying to achieve the highest sound quality with the smallest file size.  I researched and found that Midi instruments uses enormous amounts of RAM versus audio files.  
Once again, can someone explain how to change midi tracks to audio tracks. 
 
 
Sincere Peace,
Crease


      

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