You can modify all the login, image and advanced settings for BlogThing and your blog through the Configure panel.
Click
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If you can't see this button, you can either add it from the Customize panel, or select File > Configure.
The settings on the three tabs, General, Images and Advanced, can be changed in turn.
The General tab is used for setting up your blog address, the XMLRPC feed, ID and your username and password.
This is great if you've changed your blog password recently.
Use the Images tab to automatically resize images to something more manageable online (which is a good idea - it's often difficult to tell how big an image actually is just by looking at it in iPhoto).
You can also choose to upload the full-sized image as well. Be careful though as many blogs have size limitations.
Finally, the Advanced tab gives you access to more specific details for your blog.
For example, if your domain is password-protected, this is where you set the username and password.