Premium / Pro subscription plans are some older plans which are not available for purchase anymore. Users who have bought those plans can keep them as long as automatic payments are extending those plans. All the Premium/Pro features will still be available.
However, some new features, like automatic website scan, higher page scan limits, and other updates will only be available for Standard/Plus plans. If you want to use those new features, you can upgrade to Standard/Plus plans by paying the difference between your current plan price and the new plan price.
Note that you should update to a Standard/Plus plan with proper website limitations if you are using CookieScript for more than 2 domains.