how can i change the image frame/popup dimensions

can someone help me changing the image FRAME dimensions

see the image and you’ll understand

the image frame is to small. in the bottom of the pop-up there are the other thumbs and over-under of them there is a 30px space which i want to make smaller (e.g 10px) and also i want the image frame to fit the screen

(p.s i don’t mean the “detail image widht/height” from the thumbnails page. i mean the pop-up width/height