My answer: Lung function generally declines gradually in all people as we age, although smoking tends to speed up this process. Stopping smoking can prevent further damage caused by smoking. You can improve your lung function by taking medicines that help keep your airway open, such as Advair, Symbicort, Pulmicort, Brovana, Spiriva, Albuterol and Xopenex. You can improve your lung function by learning the best methods of producing a good and effective cough in order to clear secretions from your airway. You can improve your lung function by avoiding things that irritate your breathing, such as cigarette smoke, strong smells, air pollution, strong chemicals, allergens, etc. You can improve your lung function by staying physically active. Those are all things that help to keep your air passages open and clear for the smooth, easy passage of air.
However, once lung tissue is destroyed (emphysema) it cannot be regenerated. Likewise, chronic irritation may cause inflammation and eventually scar tissue develops that causes chronic changes to your air passages. This can cause permanently obstructed air passages in certain locations of your lungs.
Your best bet regarding emphysema (a restrictive disease) and airway changes due to scar tissue is to stop smoking, and you've done that. So you are well on your way to a healthier you. Good luck
Bottom line: You can improve lung function by staying positive and working with your doctor on a regular basis. However, once airway tissue is damaged or destroyed due to smoking, this damage cannot be undone. Stopping smoking, however, will prevent further damage in this regard.