@daniel12: This theme is not ideal for large header image. Maybe try other theme like Catch Adventurous.
In Simple Catch Theme, to add large image, you need to build child theme and then copy content.php file to your child theme and replace
<div class="col3 post-img">
<a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'simplecatch' ), the_title_attribute( 'echo=0' ) ); ?>"><?php the_post_thumbnail( 'featured' ); ?></a>
</div> <!-- .col3 -->
With the following code:
<div class="col8 post-img">
<a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'simplecatch' ), the_title_attribute( 'echo=0' ) ); ?>"><?php the_post_thumbnail( 'full' ); ?></a>
</div> <!-- .col3 -->
Again replace the code
<div class="col5">
with the following code
<div class="col8">
About the footer, it’s same you need to build child theme and work on it. Only Pro version give you Footer Editor in theme options panel to change the footer text.