Option called "PayPal Account Optional" is already on.
About PayPal Account Optional
When PayPal Account Optional is turned on, your customers who are new to PayPal will no longer be required to create a PayPal account to complete a purchase—they will go through an alternate checkout, and will have the option to sign up afterward. Customers who already have PayPal accounts will continue to enjoy the privileges of those accounts, such as payment history and integration with eBay Auctions, and their checkout experience will remain the same.
This feature is available for Buy Now, Donations, and Shopping Cart buttons, but not for Subscription buttons.
Note: If you have turned on Auto Return and have chosen to turn on PayPal Account Optional for new users, a new user will not be automatically directed back to your website, but will be given the option to return.