If you need support from Yola please contact us via firstname.lastname@example.org or make use of our live chat service! We are working on a new approach to community-based support and during this transition period we are not adding any new threads to this forum. Many thanks to everyone who has participated over the years and we look forward to unveiling a new peer-to-peer support system soon!
If you're referring to the Picture Gallery Widget - it is not possible to change the thumbnail size. I'm sorry. We have logged this a feature request though. I hope you can still make do with how your thumbnails are displaying in the meantime.