Remove Existing Grout
You need to remove the existing grout using removal tools like a hammer, screw driver, scraper, etc. Using a hammer, gently hit the screwdriver on the grout, to loosen it, and chip off the excess using a scraper. If you want to get done with the entire process faster, invest in a power grinder. Clean out all the debris of the old grout properly using a brush or vacuum cleaner.