Why is the top of my upper left molar rough and coarse like sandpaper? how can i get rid of this?

Sudden? Always?: At age 16, you may not have a crowned (= "capped") molar, but if it is covered with a porcelain crown, the porcelain may have chipped/peeled. If so, depending on the condition you may have your dentist polish the surface, or you may need to have the entire crown replaced--it depends. If it is your own tooth with a similar incident, you will need treatment. Need to see a dentist to find out.

Rough tooth surface: Damage to the extremely resistant enamel that covers a tooth may indicate cavity, fracture(s), developmental defect, wear from pernicious habit, anomalous anatomy, or other reasons. Go see your Dentist. (S)he has 10,000 hours of post-college training, and years of experience, to examine the tooth, diagnose what's wrong, and deciding with you the appropriate treatment.