You can easily sort references in a library on one of the fields which is shown in the short title overview.
This can be done by clicking on the in which you can find the field name (in this example starting with Author, Year, Title).
This can be done from A till Z (or old to new) as the other way around.
More possibilities for sorting you can find under Tools – Sort Library. See the screen below:
Here you can have EndNote sort several features one after the other.
Via the menu under the arrows you indicate at the topmost option how sorting must be done and this way you can go further down.
Sorting in both directions is possible.
Click on the symbol then this changes into by which the direction has changed.