You can sort the pictures in the All View by picture date or by filename. You only sort pictures manually (by sequence) within Album Views.
To change the sort order, you use the drop-down menu that allows you to toggle between the different sort orders (it toggles between the available sort orders).
You can also control the sort order (ascending or descending) for each of the methods by clicking on the Ascending menu item.
If "Sort Ascending" is checked, the the sort order will display pictures in increasing order (ex. With the Picture date option chosen, newer pictures will appear at the bottom). If ascending is not checked (i.e. descending), then newer pictures will appear at the top.
For information about how sorting by picture date works, refer to: Sorting by Picture Date
For information about how sorting by filename works, refer to: Sorting by Filename
For information about how sorting by filesize works, refer to: Sorting by Filesize