What does the premium package do?

The Premium—Campaign Monitor for Salesforce package is no longer needed and can be safely uninstalled.

You can also disregard any updates from Salesforce regarding API versions for this package—its older API version will not impact your org in any way. 

Note: With v. 7.107.0, we will automatical uninstalling the Premium package when possible.  More info.  

If you need to uninstall it manually:

• In setup, search for installed packages
• Next to Premium--Campaign monitor for Salesforce, click uninstall.
• There is no data to save, so you can agree to uninstall
• You may need to clear any blocking errors reported back and repeat the uninstall when they are cleared.