X-Cart forums - Resizing Thumbnails

Hello,
I have resized the product thumbnails in my general settings to be 150x150 instead of 100x100.

the problem i am having is i used the "Generate Thumbnail" button for some of them and those thumbnails wont expand at all. on some of my products i just used the same image for both the image (/P) and the thumbnail (/T) and those resize just fine.

so what im getting at, is i was wondering if there is a way to regenerate the thumbnails, or if there is a way to change them to use the product image (/P) as the thumbnail (/T).

Thanks in advance!
:D