Two places.  1st, some dependents need to be FT students to qualify as dependents . So that question comes up in Personal  info.  Click edit next to your dependents name.

A student only needs to half time or more to qualify for the most generous tuition credit, but full time is an option, in TurboTax.  Go through the entire education interview until you reach a screen titled "Your Education Expenses Summary".  Click edit next to the student's name. That should take you to a screen “Here’s your Education Summary”. Click edit next to “Education Information”. 

Full-time student or half-time student status varies from school to school. Per

IRS Form 1098-T Instructions, the form should have a check mark in Box 8 "Check if at least half-time student" if the college considers 6-8 credit hours to be at least half-time. Enter Form 1098-T into TurboTax exactly as it is prepared by the school.

To quickly get to the 1098-T form where you can select whether or not you were a full-time student: 

1. Type 1098-t in the search box and select the Jump to feature.
2. Continue with the onscreen interview until complete.