I know this is impossible to change from 4th what I already have reviews. But I have submitted other format is it possible to change from that to another submitted one?
Example: Suppose I submitted 3D mock up , Png and JPG in a order and somehow fiverr have taken the 3D one but I want png or jpg in the thumbnail, Is it possible to change from 3D one to png or jpg one?
Thanks in Advance 
There is a Gig gallery where you can upload raster images in jpeg, jpg or png.
The first image you upload is primary image used for Gig thumbnail. You would need to delete all images and upload again in desired order in case you wish to change the primary image.
It sucks but it´s the only way at the moment.
Thanks Dear for the suggestion but I already know that. Please at first read my problem properly . I told is it possible to change from the 4th of the thumbnails thats already have reviews in the gig.
I read this “Is it possible to change GIg Thumbnail from 4th?”
or this:
The question does not not make sense to me at all. What do you mean by 4th of the thumbnails?
I think he wants portfolio delivery images to be shown first (that is the forth image with review that shows in the bottom) and the answer is NO, you CAN NOT do it.
It goes picture picture picture than delivery portfolio delivery portfolio delivery portfolio delivery portfolio delivery portfolio delivery portfolio and that is it.
This is not TRUE.
Fiverr didn’t somehow do anything. You have control over what image will be shown in your portfolio. You have to select it properly when you make delivery.