Can I delete a dependent after the IRS has accepted my federal return?

[Kmokofisi]

I've chosen to allow my ex-husband to claim our child instead of me.

[xmasbaby0]

No.    If you claimed the child and you already e-filed you have to wait for the return to be fully processed and then amend to remove the child from your return.   The 1040X you will need will not be available until the end of March.   Since you already claimed the child, your ex cannot e-file and will need to print sign and mail his return this year.   Your amended return cannot be processed in time for him to e-file this year.

[Mike9241]

under the tax laws your ex must include form  8332 with his return. this is a form you need to fill out, sign and forward to him. https://www.irs.gov/pub/irs-pdf/f8332.pdf