If you don't have a logo to upload you can create one with our text logo tool
1) Click on the "Account Settings" tab
2) Click on the "Site Settings" subtab
3)Click on the "Change Site Logo" subtab
4) Then click "Create a Text Logo" under "Logo Actions"
5) Enter your company name and edit font color and other styles you using the tool bar
6) Click the "Save and publish" button
If you want to change in the future just repeat above steps