1. Remove all receipt numbers that are higher than the appropriate next available receipt number. For example, if the next available receipt number should be 79520, all receipt numbers starting at 79521 and higher must be deleted from the database. This can be deleted manually from each gift or by globally deleting the receipt numbers.
     
  2. Download and run the Update Receipt Number plug-in.
     
  3. Change the next available receipt number in the Receipts parameters to the appropriate value.

Alternate solution:

In the Starting receipt no. field, enter a number greater than the highest receipt number in the database. For example, if your organization resets receipt numbers every year, use a receipt number that reflects the current year (e.g. 20070001).