Glasses can become bent in a number of ways. People drop them, accidentally sit on them, and kids get hold of them. Sometimes people unintentionally fall asleep wearing their glasses and end up rolling over on them. Whatever the cause, the good news is that fixing bent glasses is usually not very complicated. It's always best to take glasses to a professional and have them repaired, but they can also be straightened at home when in a pinch.
The most important thing to remember when trying to straighten glasses is not to force them into shape. Bending them back should always be done gently so that they don't become further damaged. Broken glasses are a lot more expensive to fix than ones that are simply bent. Be sure not to apply too much pressure or use quick, jerky movements. If it's unclear which way they need to be bent in order to straighten them, place the glasses on a table or other flat surface. The side that is up in the air should be bent down. Most of the time, pressure needs to be applied at the nose piece.
The methods for working with metal glasses are different from bending plastic ones. For metal frames, use soft pliers that have ends that are covered in plastic. Place a cloth over the glasses to help prevent them from becoming scratched or otherwise damaged. Use the pliers on top of the cloth. Place them where the frame is bent, and gently ease the glasses back into shape. Take the cloth off to see if the glasses need to be straightened more, and repeat the process if necessary.
It isn't quite as simple to straighten plastic frames, because they can't just be bent back into the correct shape. Heat must be applied in order to straighten glasses without breaking them and make them stay straightened. One option is to expose the glasses to hot steam. Thoroughly dry them off with a microfiber cloth. Then, gently bend the frames back to their proper shape while they're still warm.
Another method, which is generally considered to be better, is to heat the plastic glasses in hot sand before trying to reshape them. Professionals use heated sand boxes to straighten plastic frames. Obviously, applying too much heat to plastic will melt it and could ruin the frames. Be careful about the heating method that is used, preferably sticking to one of these two options. Glasses should be able to sustain enough heat to straighten them, but take care not to overheat them.
Glasses that are bent can also be taken to a professional to be straightened. Most places will perform minor repairs like this for free if the glasses were purchased from them. When it's impossible to return to the place where the glasses were bought for whatever reason, a different retailer should be able to straighten them for a small fee. This may be the best option, especially if the glasses are bent badly, or you are nervous about trying to fix them on your own.