Caution: You can lose control of the vehicle if you try to adjust a manual driver's seat while the vehicle is moving. The sudden movement could startle and confuse you, or make you push a pedal when you do not want to. Adjust the driver's seat only when the vehicle is not moving.
Pull up on the lever located under the front of the manual seat to unlock it. Slide the seat to where you want it and release the lever. Then try to move the seat with your body to make sure the seat is locked into place.