offer discount after purchased

Hi All

using s2member and loving it so far.

On question tho i have people signed up for £5.99 per month subscriptions

is there a way to offer someone a coupon or way to give them a discount. Say if i want to give a customer already signup up paying £5.99 a 50% discount on their monthly payments is this possible?

Or do i have to get them to cancel then re-signup with the coupon?

Thanks

https://wordpress.org/plugins/s2member/