Select the group in the Module Browser or in the interface.
In the interface, click between objects in a group to select the group. You will know the group is selected if a box appears around two or more objects.
If you can't select a group in the interface or if you want to be sure to select the right group in an interface with many groups, open the Module Browser. Groups are shown in the Module Browser by name of group; if you select the group in the Module Browser, it is also selected in the interface.
Choose Ungroup from the Layout menu or the interface pop-up menu (displayed by pressing mouse button 3 in an interface window).
The objects are no longer part of the group. You can now select any of the objects and move it independently of the other objects.