Resolution of thumbnails and "show all"

Hello - the resolution of the thumbnail images on my portfolio are very low. Where can I specify a higher resolution (When you click on them they hare high res):
http://www.eastdulwichdesign.com/proof2/portfolio-item/kitchens/

And when I click "Show all" on a portfolio page it links back to a blank page.

Finally how do I hide "Published by  Kate Stuart at October 19, 2015"