Easyjet outbound flight cancelled

ah_potts

Received an email today to say our outbound flight to Malaga was cancelled but not the return flight. We have managed to book another (more expensive)outbound flight with Ryanair but still want to use the original inbound flight. 
On the form to request a refund it just asks for the booking reference and am worried that by doing this they will cancel our return flight as well. Does anyone know if we can just get a refund for the cancelled flight only and how to do this?
Thanks
Andrew