Just select PayPal at the payment screen in the checkout and then choose Pay in 3 from the options.
Pay in 3 is an interest-free loan that lets you split your basket into 3 repayments, with the first due at time of purchase and subsequent repayments due every month on the same date. Please note that Pay in 3 is a form of credit, so carefully consider whether you can afford the repayments and be aware of the possible impact of missing repayments, including future eligibility for Pay in 3 and making other borrowing more difficult or more expensive.
* Representative estimated values based on your current order total. Your finance agreement will confirm your actual deposit and repayment values when it's calculated at checkout.