Adjustment of Measures

Help, please. I wrote a score, but now want to change the value of one note in several measures, from a half note followed by two quarter notes to a full note. But I don't want to eliminate the two quarter notes. They should just start the next measure, but that throws everything off. I could redo the whole thing, but there must be a way to automate this process. Can you tell me how to do it? Thank you.