Whether you should be a member of the Church of Satan
and whether you are able to expand your power, as you call it, are not necessarily the same thing.
Membership in the COS is a very personal thing, and different persons will have their own reasons to join. Membership is not required in order to be a Satanist or practice Satanic Magic.
Learning more of the magical aspects does not require membership. It requires study and practice.
If you haven't done so, go here: http://www.churchofsatan.com
Explore everything there. Reading and understanding The Satanic Bible
is a must. Do all this first, and you will begin to understand what needs to happen. You should be able to develop other questions and post them here.
But before you do that, do spend some time looking at the forums. Often you will find the question you are about to ask has already been explored in these forums.
Onward then; you have quite a bit of work to do!