hi there! it's alright! when you select the hexcode number (the 6 digits after the # ie: #123456) you can then press ctrl+f and it will bring down a little bar with the 6 digits you selected already typed out. there should be a little + symbol underneath that, and a second text bar will appear below where you can put in the new color hexcode. after that press the "all" button and it should find and replace all the previous hexcodes with the new one! (sorry if it's a bit confusing, i'm not great at explaining this stuff)