This can by done as part of the CSV of the documents or by using the Sort By tool. 

1. Right-click on the title of a folder and then select Sort By, which will open the dialogue box and present you with the following options to sort the documents within that folder. Once you have selected how you would like to order the folder click Save Ordering.

2. If you need to move a single document, right-click on the title of the document and select Reorder. You can choose a number of different ways to reorder the document within the folder and then click Apply Ordering.