Elizabeth, Why do you say it needs regrouting? What size tiles? You can't regrout without removing the old grout. This can be a very difficult job on those closely-spaced 4x4 tiles. There are grout saws that you can use, but they will only work on larger floor tiles with wider grout joints. They'll damage wall tiles with their 1/16" grout gap. If any grout is loose and falling out then carefully remove it. There are a number of special grout cleaners that do a good job of cleaning the old grout. Use one of them (check with a tile store, not Home Depot) prior to regrouting. Mix up a little grout (toothpaste consistency) and spread it into the cracks with your fingers. Let dry a little while then wipe the excess off of the tile surfaces with a dampened sponge. Let dry fully then buff any haze off the tiles with a cotton towel or cloth.