1. Removing a single brick
To replace one brick that's in the center of many others, one method is to use a hammer drill with a 3/8-inch bit. You start at the center of the brick and drill many holes next to one another until you can take a chisel and hammer to remove the brick material. Do this from the center of the brick, working your way to the edges. Never angle the chisel toward the edges. Try always to chip the brick toward the center of the brick. This directs all pressure toward the brick you're trying to remove.
2. Tamp down the foundation
Once all of the brick is removed, smooth the sand under the brick. Tamp it with a small piece of two-by-four wood so that the sand is compacted and is at the same level as the bottom of the adjacent bricks.
3. Carefully position the brick
Place the new brick in position and start to tap it in place with a rubber mallet. You only get one chance to do this correctly. If you have too much sand in the space, the brick will sit high. If you have too little, the new brick may sit lower or will crack again if there is a hollow spot.
4. Getting the right height
The areas that are high must have sand removed to make them flush again with the rest of the bricks. Once the high bricks are lifted out of place, the trick is to use a flat board and smooth the sand. The uncompacted sand needs to be about 1/4 inch or 3/8 inch higher than the bottom of the adjacent bricks that are at the right height.
5. Use a rubber mallet and a level
You can test to see if you can tap the brick down to the correct height with the rubber mallet. Be careful so you don't beat the brick and cause it to crack. To check to make sure the bricks you're laying are not too high or low, use a straight piece of wood or a level and slide it across the existing bricks that are perfect and then onto the bricks you're working with.