See http://www.increasebroadbandspeed.co.uk/billion-7800n on how to tweak the SNR on a Billion 7800N.
It might be to your advantage to allow the circuit to resynchronise at around 1100 hours (11:00 AM) one morning.
Unless there is a GUI option which allows the link to be retrained (resynchronised), the simplest method is to power-cycle the modem/router.