How to default turn off purchase activities

When a user on my account purchases something, it creates a new activity feed post announcing that they bought something along with what they have bought. I noticed under account settings there is the option called, “Post to activity stream all purchases I’ve made” but this is set to be set to “Yes” by default. How can I set this to default to “No” for new members? Please let me know ASAP. I hope there is an easy solution for this as I did not see anything about it in the settings for this plugin. Thank you.