To add a logo to a label, do the following:
1) click on the "Account Settings" button which is the gear icon:
2) Select the picture square on the upper left-hand side. This will open a file selection tool. Just find your logo and select "open". Once the logo loads, click "update".
3) Scroll to the bottom of the Account Settings page and you'll see a section for Print Preferences. Select "include logos on labels".
That should do it.