Step 1: rollover all the IRA into a pre-tax 403b with your current employer and close that IRA.
Step 2: open a new IRA and make a non-deductible contribution of up to $6500 (or $7500 if over age 50).
Step 3: rollover the non-deductible IRA to a Roth IRA.
You will be fine. What you don't want to do is to have pre-tax money in an IRA at the same time as you add after-tax or nondeductible money. (Because all IRAs are considered 1 IRA for tax purposes, having pre-tax money in bank A at the same time as adding after-tax money to a different account at bank B could cause a problem.) As long as you get all the pre-tax money out of your IRA before you add the after-tax money, you will be ok.
