5w or 30

Hello, Just went into ASDA for some magnatec 10W/40. They only had either "10W/40 Diesel" or "5W/30 Petrol", so i was wondering if the 5W/30 would be okay for the Leon Cupra (52 reg) ?. Fairly clueless about oils other than the fact that i was recommended 10W/40 Magnatec by the SEAT dealer...