Go to the Design Studio then Images and Files where your logo is uploaded. Find your logo file, select it and then choose Replace Image or File. Choose your new logo to upload and then click replace. This will upload all emails and landing pages where you have your old logo.
Yep, just replace images like Dan said above. You may need to either refresh or clear your history to see the changes.
This assumes your logo image file is the same size and file type as the original. Replacing the file will generally work, but check to see that you match file types. ( THIS IS BEST CHOICE)
If for some reason you have to upload an entirely new file you need to update the Templates. Try to avoid that!
Design Studio > Landing Pages > Templates > Edit Template
Then update the Logo URL and any other parameters.
Test the Draft.
When happy, Approve Draft.
ALL dependent LPs will now go into Approved with Draft mode. You will have to REAPPROVE each LP before changes take effect.
Thanks, Everyone. That was extremely helpful!