To Add text that explains the Login process you can:
A: under the Module Settings-> advanced settings, you can create your own header and footer per module, with images and text.
B: Add this to the edited Login.ascx page

You will do well with purchasing one of the many modules that let you customize this.

Here is a minimal example of editing the login directly:

The actual ascx is listed in "desktopModules/Admin/Authentication\login.ascx " so you will need direct access to your installation.

Now every time you place a login module on any page it will not have the check box, remember me or register.

To fully customize this I suggest purchasing a module that allows you to do it from http://store.dotnetnuke.com

 Maybe others will also chime in.

I'm sorry, I don't understand you. could you please explain:

 A: under the Module Settings-> advanced settings, you can create your own header and footer per module, with images and text.

Where can I find these module settings?! Please as easy as possible, cause I really don't know where to find this

 B: Add this to the edited Login.ascx page

When I search my DotNetNuke-folder on this file, I find a lot of them. Which one must I have?! Or can I do this directly in DotNetNuke?