Try Raising the seat
Do it as follows--but make sure you wear the shoes you normally wear when cycling

1 Loosen the seatpost nut (by flipping up a lever, as shown here, or loosening the nut with a wrench).

2 Pull the seat up by twisting it back and forth.

3 Put the bike next to a wall or have a friend hold it. Then sit lightly on the seat.

4 Put one pedal at the 6 o'clock position, and put your foot on it.

5 Your knee should be slightly bent. If it isn't, change the seat height. (If you end up with less than two inches of the seat post inside the frame, you might have to get a longer post. Otherwise, the bike is simply too short for you.)

6 Tighten the seat post nut