It's not up to you to decide whether or not your parents can claim you as a dependent. There are rules about who can be claimed as a dependent. Do you meet all the requirements for them to claim you? There is a summary of the requirements in Table 5 at the following link. The details of each requirement are explained in the text below the table.
https://www.irs.gov/publications/p501/ar02.html#en_US_2016_publink1000220868
If you don't meet the requirements for your parents to claim you, you do not have to change anything. If you do meet the requirements for your parents to claim you, you have to indicate on your tax return that someone else can claim you as a dependent. You will then lose the personal exemption for yourself, and your standard deduction may be reduced. These changes will most likely increase the amount of tax you have to pay. If you already got a refund, you might have to pay some of it back.
Since you have already filed your tax return, you will have to file an amended return to make the change. An amended return has to be filed on a special form, Form 1040X. It cannot be e-filed. You have to print it and file it by mail. It takes the IRS up to 16 weeks to process an amended return.
Don't file the amended return until your first return has been accepted and you have received the original refund.
Go to the following link for instructions to amend a 2016 tax return that you filed with TurboTax Online.
https://ttlc.intuit.com/questions/3402261-how-do-i-amend-my-2016-turbotax-online-return
When you get to the point in the amending process where you actually make the changes, go back to the Personal Info section and check the box that says someone else can claim you on their tax return. That's the only change you have to make.
Even after you file your amended return, your parents will not be able to e-file if they claim you as a dependent. The IRS files don't get updated quickly enough to let them e-file. They will have to file their tax return by mail, with you claimed as a dependent.
