To upgrade, go to the store and click on the category "Upgrades" where you can select the product. Note, these products are at full price and the price difference will be recalculated at checkout.

Select the product you want to upgrade to and click "Buy now". Then on the basket page enter your old activation code - this will subtract the amount spent on your current license from the new product so that you only pay the difference.

Click "Purchase" and continue. Note that after successful payment your old activation code is automatically deactivated.

Note also that Pamela Professional and Business have a recording import function. This allows you to import your old recordings to Pamela which makes upgrading from e.g. Pamela Call Recorder much easier.