Be aware that if you cancel either the 461 or the bridging visa, it's best to do that from outside Australia, otherwise you'd immediately be here illegally. You may also find the study visa has more restrictive conditions than either 461 or bridging visa. So unless your relationship with your partner has broken down (and you're no longer eligible for the 461) or your bridging visa doesn't include study rights, it's unusual to cancel either of these.