NOTE: If you want to know how to make a circular about me image, view the Circular "About Me" Photo tutorial.
An About Me widget is built into your theme. You can find this widget by going to Appearance > Widgets in your wp-admin.
1. Find the About (your theme name) widget and drag it to your desired widget area (such as the sidebar).
2. In a new tab, open the media library by going to Media > Add New in you wp-admin.
3. Upload the image you want to use for your widget, then click Edit located on the right hand side of the image.
4. You'll be directed to an Edit Media page.
Copy the File URL on this page, then go back to the widgets page.
5. Paste the File URL that you copied in the Image URL box in the About widget.
6. Enter your image width and height in the appropriate boxes, as well as your blurb in the About Description box. Remember to save your changes.