Moving from Ning
Ning To Jamroom
Default images in Jamroom skins can be replaced under the skin's image tab.
From the ACP=>Skins=>'your active skin'=>Images
Upload a new logo.png image file, click Save at the bottom of the screen, clear caches if necessary.
Tip - When developing a site put it into 'Developer Mode' (ACP=>Modules=>Developer Tools=>Global=>Developer Mode). This disables caching so any changes you make will show immediately.
hth
Paul