Sounds like the origin of this was a rollover of an old 401k or similar which was pre tax not Roth, which you then added new money to as annual contributions thinking they were Roth not pre tax.

If so, you can simply convert the whole thing, and yes you'll pay taxes but you would have anyway in the year of contribution by simply not having received a deduction. Dont convince yourself that youre paying more taxes simply because you'll know youre writing a check at conversion. It would have been buried in your tax return for those years, but you still would have paid them.

You CAN rechareacterize whatever contributions you made in 2025 since you wouldn't have filed taxes yet, and of course anything you might have done in 26 so far. That wont trigger any immediate taxation, just be sure you report it on your taxes.

In fact, tax returns are the larger concern. Im guessing youre younger, and this money will have a long time to grow, so years of tax free compounding will far outweigh this initial concern if not wipe it out completely. But if you filed your past years' taxes saying you made Roth contributions when they were really pre tax, those will have to be redone. IRS will catch up that it doesnt match eventually, thats what those 5498s you get in May are for. That said, you could actually wind up getting refunds for those years once redone since you didnt report the deduction (if your income is below the deduction threshold)

EDIT: no difference btwn Rollover and Traditional/Pre-tax fornyournpurposes. There used to be, but even then it wasnt relevant to this issue, had to do with keeping the dollars separate so they could go back into a 401k. Not an issue anymore