You can add or change your logo by mousing over your organization's name in the upper right corner and clicking on Account. You will then see the currently logo or generic image on the left corner of the page.




Right below the image there is a grey button that says "Update Company Logo", 
Click the Update Company Logo text to select a logo that is saved on your computer. Navigate through your documents and folders, and select the image that you would like to use for your logo. Click on the image you want to use and click open. Your image will replace the image that was originally there. You can change your logo at any time and as many times as you would like, by repeating these steps.