In this case you can order both sizes and try out and compare them at home. The ones that does not fit, you can just return.
We are interested in this boots http://www.footway.no/wooli-3bw-winter-cognac.html , we would like to know if we order them and the size too big or too small is it possible to get a change after?
We have found the measurements for the foot sizes for this brand on their web site, and my wife is on a limit between size 39 and 40.
And our concern is that the 39 may be to small, or 40 to big.