Open the transaction area you wish to to change the number of. For example, if you which to change an invoice number, open the invoicing area.
From the menu select Toolbox|Change Transaction Number.
Enter the new transaction number and press Save.
If you wish to change the transaction number for the present transaction and also the transaction sequence permanently, tick Set As New Sequence.
Re-run the above tool to change the number or sequence again.
NOTE: You must have administrator access rights to be able to permanently change the number sequence.