Whether you have an FFEL or a Direct Loan, you are entitled by law to adjust your repayment plan any time.
If your student loan debt collector isn't working with you on changing your plan when and how you want, they very well may be in violation of the Fair Debt Collection Practices Act! That might entitle you to compensation and give you significant leverage over the collector and the debt.
The U.S. Department of Education offers a good overview of the different available repayment plans, as well as a list of the most common federal loan servicers along with contact information.
Remember: Just because your loan is delinquent or in default, collectors are not allowed to ignore your right to select and change repayment plans!