Change in Circumstances on JSA

Do i just ring them? hubby and I split up before xmas, he is claiming IS as he had the kids while i worked F/t - i was made redundant in jan, and have been claiming JSA for myself.

We have decided to give the marriage another go, so i plan to move back in to home, obv his IS will stop, so i need to change the JSA to a joint claim. Can i ring them, or am i better to do it face to face when i sign on on friday?

thanks in advance!