Unfortunately an account cannot be cancelled, deleted or merged with another account. You can clear all the information from an account and leave it inactive.
Sign in to the TurboTax Online account that you want to leave inactive and open your return by clicking the orange Take me to my return button.
With your screen maximized, click My Account (at the top of your screen toward the right) and select Clear & Start Over. (If on a tablet or phone, you may find the Clear & Start Over option by clicking the three parallel lines, or “hamburger”, in the top left corner.)
Answer Yes to Are you sure you want to clear your return?
After your entries have been cleared out, you can exit the account and leave it inactive.