Remove or Reassign Sign Up Button?

I am using the member plugin with the community theme. I have found how to reassign the sign up button in the welcome message section to my member plugin registration page.
However, how do I remove the Sign In button on the header? (Image attached). Or, if it is easier how do I reassign the page that this button points to so that I can have it take the user to the member plugin registration page as well?