For Transaction Numbers, it is automatically generated or assigned when user creates a Transaction. The number that is assigned is the next one on the sequence based on the last assigned number.
To be able to edit or change the number assigned, kindly do the following:
1. As Administrator navigate to Setup > Company > Auto-Generated Numbers.
2. Go to Document Numbers tab.
3. Mark the Allow Override checkbox for the transaction user wants to edit.
4. Click Save.