Cannot edit category.php file to add description – Theme: Evolve

Hi guys,

I am using Evolve theme, and this theme by default does not show description when you create a category. I read this morning I could add this line to the file category.php

<?php echo category_description( $category_id ); ?>

But the point is that I went to the file manager in my hosting provider space, I downloaded the file for edition, and once edited, I cannot upload it back to the path where the file is originally – /app579635552/wp-includes –
I am getting the message “You cannot write in the upper directory” (or something similar, i get the message in spanish).

Can anybody help me?

Thanks
césar