Since freckles are almost always harmless, there is no need to treat them. As with many skin conditions, it's best to avoid the sun as much as possible, or use a broad-spectrum sunscreen with SPF 30. This is especially important because people who freckle easily (for example, lighter-skinned people) are more likely to develop skin cancer.
If you feel that your freckles are a problem or you don't like the way they look, you can cover them up with makeup or consider certain types of laser treatment, liquid nitrogen treatment or chemical peels.