This is just an educated guess. I would say your weight would be lower as you move closer to the center. Your weight would be approximately zero at the center. Your mass is always the same. Gravity is the phenomenom where mass attracts mass. On the surface the earths mass pulls on your mass. In the center you have equal mass all around you. If you went down a perfectly straight tunnel, there would be slightly more gravity below you than above you. probably not enough to measure. I would expect the gravity pulling from all sides would blow you up like a balloon.