[nextgen-gallery] Album Thumbnails and Captions Are Crowding

The thumbnails in my album are crowding each other and the captions are overwriting the thumbnails. See the page here:
https://www.burgetteart.com/new/carvings/interpretive/

I need larger thumbnails in the galleries themselves to better showcase the artwork, so resizing the thumbnails is not an option. How can I specify the thumbnail size for the album display?

Thanks,
Lori