There is a lot of misconception when it comes to removing grout from tiles. Regrouting is a very risky procedure as you or your tradesman can easily damage the tiles edges. If you have no spare tiles then it is even more riskier. The methods in removing grout vary as it mostly depends on how hard the grout is installed. The softer the grout the easier it is to remove.
To test this simply use a pocket knife and press down hard or scrape to see the strength of your grout. If your grout is rock hard which is what you want your grout to be, then only a grinder with a diamond blade would work but again this is a risky procedure. A safer option is colouring your grout using a professional premium grade grout colourant. Forget about cheap grout pens and epoxy grout colorants. You need a grout colour sealer that sticks and stays and most important looks like grout not paint.
The only reason you cannot recolour your grout is if your grout is to high not recessed below the tile. Some tilers do not recess the grout during the installation which is just plain lazy as they are suppose to use a rounded sponge to recess the grout before it cures, they only use their grout float to recess which is not the right process.
I cringe when I see a tiler do this as they are creating major problems for the owners when it comes to maintaining tiled floors. High grout joints that a level with the tile makes it impossible to keep clean as everything catches the high grout joints such as foot traffic or dirty mops. Your only option if you have high grout joints is to replace the floor with new tiles or re grout but just make sure you have spare tiles just in case they are damaged. Perfect recessed grout joint below.
People often ask us! Why is grout colour sealing better then new grout being replaced. New grout may look nice when new but it is 100% porous and will not look that way for long. Grout colour sealing lets you change to your desired colour, gives you that uniform look and the best part it is sealed. This is the safest and cheapest option then having your grout replaced.