Unfortunately the only way to know for sure would be DNA testing. Lord Snow's body was burned upon his death as per the customs of the Nights Watch at the time and even if it wasn't, the Starks have forbidden access to the Winterfell crypts. That being said there are several currently competing theories among historians, however without additional information being revealed it is impossible to say which one is correct since they all rely on secondhand sources usually from someone who had an interest in having a connection. It is rumored that the Reed family has in their possession document(s) which would resolve the issue but they have not yet seen fit to release them.