There are two ways to do this.
1. Just withdraw the money as a regular withdrawal. Withdrawals of contributions from a Roth IRA are tax-free and have no time limits. Then, make an independent contribution to a pre-tax IRA.
2. You can recharacterize the Roth contribution as a deductible traditional IRA contribution. This may require that the same bank/trustee hold the traditional IRA and the Roth IRA account.
The financial incentives are complicated. You have the immediate tax deduction (withdrawals fully taxable in the future) compared with no deduction but the withdrawals are tax-free. There are also some sound reasons to have your money spread out between Roth and traditional IRAs when you retire (not all in one kind or the other kind).
