Re-sizing thumbnails

Hi

Does anyone know how to re-size the thumbnails that are generated? The ones it is making for me are too small and if possible I would like to change the aspect ration too.

Interestingly, the thumbnails it is generating are smaller than the ones on the Gallery Types demo page: https://www.nextgen-gallery.com/demos-of-all-nextgen-gallery-types/ so some re-sizing must be possible.

Thanks very much.
JG

https://www.ads-software.com/extend/plugins/nextgen-gallery/