If you claimed your own personal exemption (box 6a) on your tax return, the only way to change it would be to file an amended return (1040X). You can do that in TurboTax.
You'll need to wait until your original return has been processed by IRS and any refund issued. Then you can prepare the amendment and make the necessary change. You will do that under the Personal Info tab by answering "yes" to the question, Can someone else claim you as a dependent on their tax return?
The IRS doesn't accept amended returns via e-file, so you'll have to print, sign, and mail it to them.
Here's the link to the TurboTax support page for amending returns, which will get you started: https://turbotax.intuit.com/tax-tools/tax-tips/IRS-Tax-Return/Amending-Your-Income-Tax-Return/INF120...
One last thought: you mention that your mom had to "redo" her taxes because of your return. Understand that even if you amend your return, the only way for her to benefit would be to file an amended return of her own, claiming you. It's a two-step process: first you amend and don't claim the exemption, then she amends and claims you.
