I had called around to have this done in my bathroom . The cost was prohibitive. So......When I did this, I purchased a Dremel tool to make removal of the grout easier. ( tried the hand tool but wound have taken weeks and to much elbow grease) Go slowly and be careful not to damage the tile. Regrouting was the easiest part. I did small sections at a time of grout with epoxy in it. Epoxy grout is more expensive but it is also more durable and stain resistant. It dries relatively fast so I ended up applying it to small sections with my finger and cleaned it up as I went along. Doing grout removal is time consuming but it is not difficult Good luck!
If it's the color you don't like, you could try something like a grout renew pen.
Do you want to change it because you do not like the color, or does it need to be redone because it is worn out, and no longer adhering adequately?
Try painting it! https://thehoneycombhome.com/painting-grout-how-to/