Hope you are using child theme that comes with zip file of themeforest. To change image dimension you can do it through child theme.
If you have not used child theme please install and activate child theme and follow following process:
– At functions.php of child theme please add: add_image_size( 'blog-way-large', 690, 450, true );, You can change image size of your own.
– Create folder name ‘template-parts’ on child theme directory
– Copy content.php from child theme and paste into that folder.
– Go to line 16, you can see following code: <a href="<?php the_permalink(); ?>"><?php the_post_thumbnail('blog-way-plus-common'); ?></a>
Replace it with <a href="<?php the_permalink(); ?>"><?php the_post_thumbnail('blog-way-large'); ?></a>
Hope this will help you. Feel free to use our support forum or online chat if you need further help.