You can write a codicil to your will but I can't suggest the wording unless I know where you want your money (or other bequest) to now go, as that could affect other parts of your will. (e.g. if your current will divides everything equally between Fred, Mary and Joe but you now want only Fred and Mary to benefit equally, then references to what Fred and Mary get will need to be changed).
If a draft of your will is stored on your computer though (as mine is), it would be far simpler just to modify that document to produce a new will.