1. From within your TaxACT return (Online or Desktop) click on the Federal Q&A tab
2. Click Education to expand the category, then click All education topics
3. Click Yes on the screen titled Higher Education - Education Expenses, then click Review 
4. Continue to the screen titled Student Information - Dependent Exemption to review or change your selection

If you want to indicate that you can be claimed on someone else's return: 

1. Click on Federal Q&A tab
2. Click on Basic Information in the left column
3. Click on Dependent on someone else's tax return and follow the prompts on the next screen.