Leaderboard

Hi everyone, I've just started using Blesta, and have been working my way through getting it right. I've gotten to the user registration form - there are a few fields I really don't need from clients, and I was wondering if I can switch them off? Similarly, I'd love to be able to add one extra field (checkbox) and hook into it when they submit (an API for a newsletter) - is there any defined way of doing this / could anyone point me in the right direction? Many thanks!