In November 2017, I purchased the basic annual plan and now I want to upgrade it, but already paid $69. Will I receive a credit for the unused balance when I upgrade to the premium membership?
As per the description above, you want to upgrade your current Acrobat Plan, Is that correct?
Please refer to the following KB doc to know more about the upgrade options Manage your Creative Cloud membership Link: https://helpx.adobe.com/creative-cloud/help/manage-cc-individual-membership.html#view-upgr ade-change
You can also contact the Adobe support team for detailed information about available upgrade options https://helpx.adobe.com/in/contact.html
Feel free to update this discussion for any further assistance.