Do you have experience with using CSS or manipulating the php files?
I have moderate css experience but very little php.
To change the thumbnail size generated across the board, I would recommend starting here (https://codex.wordpress.org/Post_Thumbnails) to learn more. After changing that in functions.php, you would need to regenerate your thumbnails (via a plugin) to show those changes.
Something to double check is that your img are currently set with a typo in their ‘height’ – it should be auto but there’s a number stuck in there on accident. Fixing that might help!
Taking out the descriptions would be a theme-based php change.
@nabonga: You’re using a premium/paid theme. It’s best to go to the support site where you bought the theme http://www.mhthemes.com/ for help with customizations and issues. You paid for support when you bought the theme, so you should contact the people who sold you the theme.
These forums are for free themes available in the WordPress theme directory at http://wordpress.org/themes/. See http://codex.wordpress.org/Forum_Welcome#Commercial_Products
