If your glasses need serious adjustment, take them to a professional, but there's a lot you can do to make yours more comfortable at home. Maybe they rest a little too low on your nose, or they pinch a little bit, or they're a little crooked. This graphic shows you how to handle all of those issues.
The graphic, from the folks at Zenni Optical (who of course, have a vested interest in you buying their glasses,) actually shows you how to make sure the ones you have are as comfortable as possible. They break their advice down into tips for wireframe glasses and for plastic or acetate frames separately, so you can choose which works best for your frames. If you have the latter, you may need the help of a little warm running water to make your frames a little more pliable without the risk of breaking them. Check the whole graphic out below.
How to Adjust Your Eyeglasses Infographic [Zenni Optical]