How to customise membership pages?

Hi,

I'm struggling to find how I can customise my registration pages to fit the style of my site.

I don't want to use the default layout and when I go to edit the page there is nothing there to amend/change, just an empty post field.

I can add text to the page via the post field but this only includes it above the membership options in the front end, it doesn't replace it. There doesn't seem to be any way of editing/removing the default button/layout.

Can anyone help?