If you have deleted PayPal transactions either in the staging area or that have already been imported then you will need to re-import these.
If you have deleted transactions and would like to reimport them you will need to delete everything you have imported up to the date of your earliest deletion.
For example, if the current date is 01/07/2013 and your earliest deletion is 01/03/2013 then you will need to delete everything that has been imported via PayPal for 4 months (01/03/2013 - 01/07/2013), this is to avoid duplication when re-importing.
Now you will need to go to the Paypal settings area by going to the Overview page and then going to the Imports section. Here you will need to press the little Pen and paper icon to open the settings page. Now you will have to change the Start Date to the date you need the transactions from, at the bottom of this page you will see the option to Update and Re-Import.
The importer will now start and the transactions will appear in the Staging Area once completed.