If you are still experiencing ads on your device after upgrading to Pandora One you may need to verify that you are signed into the correct account.
 
You can find the active account by opening the app and going to the Station list.  At the bottom right you'll find the Settings area.  Once you open your Settings, you'll see the email address next to the Account field. If this is not the correct account, scroll down and select Sign Out.
 
Then log back in with the upgraded account.