You can easily sort references in a library within one of the fields which is shown in the short title overview.
This can be done by clicking on the bar in which you find the field name (in this example starting with 
Author, Year, Title, etc.).
This can be done from A till Z (or old to new) as well as the other way around.
More possibilities for sorting you can find under Library - Sort Library. See the screen below:
Here you can choose to sort several fields one after the other.
Use the drop-down menus to indicate how sorting must be done.
Sorting in both directions is possible.
Click on the symbol 
then this changes into 
by which the direction has changed.
