Go to your blog area first http://www.tumblr.com
Now we will go to blog area to add or change. Login using your details. There is already there one which is published.
You can edit the current one or delete it.
Any changes will reflect online instantly.
Now we will try adding image blog or any other blog. You can try Text blog or link or chat or audio blog as well .
After uploading image from my machine .
And simply press Post.
Once its added then refresh your site