change the numbering on contracts

[cj12345]

how do i change the default numbering system in contracts? It sent a test one to myself, and although there is nowhere to edit or even see a number before it is even saved as a draft, the email i received (as a test client) said "new contract: #000001 [title] from [business]". How unprofessional. I do not want to send my client invoice #000002. How do i change this??