To transfer your Direct Access time towards your Banktivity 8 subscription you can go to File> Subscription> View My Subscription. There you should see a button available to transfer your remaining Direct Access subscription time towards your Banktivity 8 subscription. You will need to start a subscription in Banktivity 8 first.
Note: You will still be able to use your Direct Access time in Banktivity 7 after upgrading to the new Banktivity, but you should make certain you are not syncing your v7 document with your v8 document. Please take a look at this article if you are using Cloud Sync in v7 and are planning to upgrade to the new Banktivity: