This article explains how to change your Gmail account photo. Once set, your profile picture will be used to identify your account in chat lists, your contacts' address books, your Google+ account, as well as with the emails you send. You can set and edit your Gmail avatar in a few easy steps.
How To Change Your Gmail Profile Picture
Sign-in to your Gmail account, click the cog icon and select Settings. Next, head to the General tab, scroll to My picture and click on Select a picture:
Select an image from your PC and upload it. You can use any JPG, GIF or PNG file. Crop the image if needed and then click on Apply Changes:
The last step is to set the visibility of your profile picture. Select between Visible to everyone or Visible only to people I can chat with: