To clear loaded images in a picture box- C#

Question

Hello experts,                                                                                                                                                Initially i will be loading images(say 20images) into a picture box from a specified folder through selection from combobox dropdown , they get loaded normally into picturebox. The problem i am facing is when i select the next folder to acquire the image for processing, the previously selected folders images are also displayed in the picturebox after its count only the next folders images are displayed, i am unable to clear the previously loaded images. To be specific, when i click on a folder from dropdown i want the particular folders image inside the picturebox i dont want the previously loaded images along with them. Am working in VS2013 with c#. Thanks in advance.