To add it to any existing forms:
- Edit the donation form
- Go to step #3 Design Donor Screens
- Edit the Donation Form
- On the right box, you'll see a list of items that are on the form, you'll look for 'Payment Type'
- Select the Payment Type and click the 'Save Order and Edit Selected'
- Once in that step you'll look for the option to 'Allow payment with PayPal:'
- Check the box to 'Yes, allow donors to pay with PayPal.'
- Click Save.
Now that form has the option to pay with PayPal.