The time between your statement date and the day your payment is due is changing from 25 or 28 days to 20 days. This means if you are paying interest, you will be charged less interest on your existing balance.
If you pay by Direct Debit, the date you pay your card is staying the same and your money will come out of your account on the usual date each month. If you pay manually, remember to keep paying on the same date as you usually do.