Here are some solutions to help you adjust the fit of your mask to make it more comfortable for your face and ears.   

If you'd like your mask to fit looser/larger:

First, open up all of the pleats and really stretch the elastic out on both sides. Depending on the size of the elastics on your masks, there are either 3 larger bands or 4 smaller bands on each side.  You can snip the middle band(s) and you will be left with 2 loops sewn into the mask (picture 1).  With those 2 loops, you can add a strip of nylon (picture 2) or a narrow piece of ribbon (picture 3) or flat/round elastic cut to the exact length that you need.  For the nylon, you can cut strips from a pair of pantyhose.  It sounds weird, but it works because there is some elasticity to it and it is really soft against your ears.  Additionally, you could make ties out of ribbon/shoelaces/etc and attach them to the loops (picture 4).  Then you could tie the mask around the back of your head to keep it in place.  Depending on how long you are wearing the mask for, having different ways of wearing it may be helpful.  

    

If you'd like your mask to fit tighter/smaller: 

Pull the middle elastic band(s) and make a knot.  (picture 5).  This will shorten the ear loop and pull the mask in closer to your face. 

picture 5: