When you go to specified order, you must enter each value into the area "Named Group"--you are naming each instance of the group, not the group itself. So if your group field is quantity, and the instances are 1,2,3, and you want them in order 1,3,2, then place 1 in the named group field and enter, 3 and enter, 2 and enter. You don't have to use the new and edit buttons if the group instances are already defined. If, however, you wanted to cluster results into groups, you would enter "1 and 3" as the named group and then press new and define it as one of these numbers.
To reorder entries in the original screen, just use the direction keys.
If you have only numbers in your field, and they are sorting like text instead of numbers, you could convert them to values first (val({text.field})) and use the formula in the crosstab instead of specified order.
-LB