The Thrift Savings Plan (TSP) is a retirement account that is available only to members of the armed forces and federal employees. As with a 401(k) plan at a private company, funds accrue in a TSP as contributions that are withheld from your paycheck. Some agencies also make contributions to employee accounts. You can change your contribution amount at any time, and can repeat the action as many times as you like. No fee is charged to change your contribution amount.
Download and print the election form from the TSP.gov website (see Resources).
Complete the form with your name, address, phone number, office, Social Security number and the contribution change. You can change either by percentage or by dollar amount. You can contribute up to the elective deferral limit. For 2011, that amount is $16,500.
Sign at the bottom of the form and turn it in to your human resources or personnel office. It can take up to two pay periods to see the change reflected.