I've found a rather straight-forward and not too highlighted method for members that, having filled their quota of deviations, would after a time want to remove any number of them to substitute the pertinent pieces, at their leisure, with newer and better work.
Go to a deviation you've submitted to the Group and want to remove from it. Click the "Edit Deviation" button.
On the "Edit Deviation" page you'll find just under "Category" the Groups where your deviation is currently displayed with a remove button (a white "X" on a red circle) beside each instance.
If you do so desire, click the pertinent remove button after which the message "The deviation will be removed from #Paleoartists when you save these changes." will appear along with an option to undo.
If you want to go through with it, do as the message says and save the changes.
Mind you, the minimum residence time for a deviation in this Group is one month.
I hope that was thorough enough, but if you have any doubts feel free to ask in the comments.