If you don't have any baddies on your report, just high utilization, then all you need to do is to get your utilization down (I know easier said than done). FICO doesn't have any memory. Once your utilization is below 30% (ideally below 10% on one card, all others at $0), you will have a very nice FICO score. FICO really punishes your score if you have maxed out credit cards.
PS. As you finish paying off your credit cards, don't close them without asking for advice first.