First, you need to already own a Vocaloid2 voicebank and the Vocaloid3 Editor. Next, open up the folder where the Vocaloid3 Editor is placed and click on ImportLib (you need the admin's permission to continue). Select your language and check the voicebank you want to import. Click on the VOCALOID STORE button in order to import the vocaloid's serial code and get a new serial code for importing the voicebank. Put the new serial code in the boxes below. You should be fine from there.