My words on my computer got super small! cant figure out how to fix it! please help?

ONE DAY THE LETTERS WENT REALLY BIG, THEN SO SMALL I CANT READ 1/2 THE STUFF IM LOOKIN AT! YIKES! AS FAR AS I KNOW I DIDNT TOUCH ANY THING! KINDA SUCKY! CAN ANY ONE HELP ME?? THAT WOULD BE GREAT! THANKS AGAIN.