Changing login at Sign Up button

Hey guys,

I'm currently using Membermouse for membership plans and would like to know how can I change the the link address from the SIGN UP button that I find when I click on DETAILS in courses area.

I want to centralize all kind of registration on Membermouse, for that I need to change these link buttons

here's the link - http://courses.nativeportuguese.co/courses/verbos/