I do believe that for $25 you can purchase the 20 Ways Template Conversion Pak which should explain or provide how to change the Combined Login page.
Otherwise, to do it yourself you would be working with these files:
includes/templates/template_default/common/tpl_main_page.php
includes/templates/template_default/templates/tpl_login_default.php
includes/templates/template_default/templates/tpl_modules_create_account.php
includes/languages/english.php
includes/languages/english/login.php
The learning is in the doing.
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