Reply To: Portfolio lightbox doesn't work with Optimal v1.3

I’m referring to the 2 kinds of thumbnails:
(1) theme thumbnails, where you can change the size on the Media Settings page. The default is 150x150px.
(2) portfolio post thumbnails, which can be resized in functions.php.
I’ve tried changing both of these thumbnail sizes to 300x214px, with and without cropping to achieve the desired results. The results are inconsistent. Some don’t resize. Some resize but the resolution is at the smaller 150x150px level. Some resize but stretch the image and distort it.

The image’s original proportions should remain intact, so cropping ok. I’d like the 300x214px size. Do I have to regenerate the thumbnails somehow?
Thank you…