Unfortunately you cannot transfer the funds from those cards to your PayPal Account Balance. All you can do is use the cards for purchases.
Note, make sure you register your name and address with the card issuer before you attempt to link the cards to your PayPal Account. (The name and address must be the same as used for your PayPal Account setup, else you will run into issues, PayPal does not always play well with prepaid type cards.)
