Changing and editing page templates. ie: sentences and buttons

I have set up Membership and I have had no problems with setting up the functioning of the site.
What I am having problems with is that I really want to change some of the verbiage such as "We have the following subscriptions available for our site. To join, simply click on the Sign Up button and then complete the registration details."
I only have one subscription level.
Could you please direct me into the right direction to fix this?