The theme does not come with any feature to change these sizes, so keep in mind you’re sort of moving into the grey area of making customizations.
You can use this plugin to change the height of the image crop size, but keep in mind it’s a sort of “edit at your own risk” kind of deal. 😉
In the Theme Blvd Image Sizes plugin, the “1/3 Grid” image crop size is what’s use for that slider type. After changing the size, you need to make sure and re-generate your thumbnails, and re-save your slider.