It depends what you mean when you say mess....If it's simply looking shabby, walked on, scuffed & with some bare patches I'd be inclined to repair rather than replace. Give it a good raking & scatter some seed in the bare bits....it's amazing how lawns recover at this time of year (unless you live somewhere extremely cold).
However, if it's wrecked with humps & hollows you could still replace this year. Turf it for instant effect which will need good preparation....(old grass removing, levelling & firming etc) or seed it, but for best results you'll need to get your skates on I'm afraid ....erm, not literally, not on a new lawn! :o)