As previously mentioned, pick up a copy of the Lyman manual. As to a larger mould, you could enlarge the existing cavities by taking some of the bullets you have already cast, drill a hole partially thru them, take any type of screw, of the appropriate size, and screw it into the hole. You want something that you can chuck into a drill. Now take so sort of MILD abrasive and put this on the bullets. Put the screw into the drill chuck and SLOWLY turn the bullet in the mould, checking often. You don't want to take off to much material, it's not like you can put it back on.
Try this on one cavity and if you're pleased with the results, do the other.