We have a basic guide here:http://www.minibb.com/synchronizing_minibb.html
But you must be a coder to get your membership adjusted. It's not about the pre-composed code.
Here is a guide for WordPress users
Sorry, I have no ideas what your website is built on, what kind of authorization it uses etc., and how it is possible that you already have a code from smf, meaning smf is the same kind of software like many others. By the way, it doesn't mean at all, that if you have some code for smf, it would work for you. Not at all.
So you possibly understand that we can not give you a precise guide. This may be a very customer-related task and the exact result comes only in terms of our paid support.