3D FlipBook - Make Thumbnail bigger

Hello how can i make the Thumbnail bigger Size : Like this on the right Site https://prnt.sc/26vgnh0

I have changed in the Setting Medium to 400X400 https://prnt.sc/26tvlab

After that i have updated https://prnt.sc/26tvmio

and it still 150X150 but the Picture Size is more then 300X300 https://prnt.sc/26tvnb6