I know its an old thread but I need help with the same thing.
I copied the general-register-modal into the child theme folder.
Now to remove the full name part do I just remove the following text?
COPY CODE
<div class="six columns">
<input type="text" id="fullname" name="field_1" class="inputbox" required placeholder="<?php _e("Your full name", 'kleo_framework');?>">
</div>
Thanks