Is the grout coming out? Need to be replaced? Or just cleaned?
If you need to replace: you can go to your local hardware store and purchase the color grout you would like and simply go over your current grout
Re color your grout: I used this product before in one of our bathrooms and it worked great!! 6 years later no issues! it comes in lots of colors
Clean your grout: this is my favorite grout cleaner recipe: http://gatheredinthekitchen.com/category/craftsprojects/painting-staining/
What's wrong with It? Dirty, falling out???
You can remove with a grout removal tool, then put new grout in its place and seal.
Hello Eileen: Here is a site that may help you: https://www.westlakehardware.com/videos/ask-the-experts/what-is-the-best-way-to-remove-grout-and-regrout-tile/