how to increase the resolution of group thumbnail images

[bradthor]

How can I increase the size / resolution of the social group thumbnail images and how do i stop the images from being re-sized when I upload them during the creation of a group.
Any help would be awesome.
Thanks

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i need to change image.php?groupid=6&dateline=1452004739&type=groupthumb
to
image.php?groupid=6&dateline=1452004739
in group thums How do I do this?