I have a few cracked tile in my kitchen (floor). How do I remove them? I have a few pieces in the attic to replace them and I really think I can do this. Also, in another area, some of the grout is out. Do I just take a few of the grout pieces to a store to match up the color? The house is only about 8 years old.

Cracked tile and chunks of missing grout are almost always indicators of movement in the subfloor under the tile, usually in the form of deflection (think bounce).You can replace the tile and you can put new grout in but none of that will fix the problem and it will all start to happen again. To match the grout you can take a chunk to the tile store but there are several grout manufacturers so you need to match up the maker as well as the color. Before you go digging up the old tile tell us what is under the tile now. Is it a wood framing floor or a concrete slab. If wood, how big are the floor joists, what is their spacing and how long is their unsupported span. Is it plywood under the tile, how thick? Or is it OSB or pressboard? Any cement board over the plywood? There are several reasons for floor movement and my questions are an attempt to isolate what specific reason there is for the tile failure. I will have more based on your answers.

It is just a concrete slab. I have several cracked tile.

That makes it a little easier.

To remove a tile you first have to isolate from the surrounding good tile to remain in place. To do that you must remove the grout from all sides of the tile about 2/3 of the way down into the grout joint. There are some grout removal tools at the home centers but it is a tedious job. To remove the tile, create a few more cracks by hitting it in the middle with a hammer. Thyen use a chisel or stiff putty knife to get under chunks of cracked tile and lift or pry them up. Important thing is to work from the middle out to the edge so you dont chip the side of a neighboring tile. After the tile is removed the thinset under it has to be scraped off the cement floor and make the floor smooth. You will probably discover that there is a crack in the floor right about where the crack in the tile appeared. If so, this must be addressed with a crack isolation membrane so the crack does not come back. If you choose not to use one the crack may very well transmit up again into the new tile.
If there are no cracks under the tile then it may have just been defective coming out of the box, or not enough thinset was used under it when originally installed, and no membrane would be needed. Get some modified thinset and bed the new tile in the thinset getting full coverage on the back of the tile so there are no voids or airpockets under it. After it dries the next day, put the new grout back in.